# Top Level Namespace

## Included Modules

- Spec::Expectations
- Spec::Methods

## Extended Modules

- Spec::Expectations
- Spec::Methods

## Defined in:

## Constant Summary

ARGF = `IO::ARGF.new(ARGV, STDIN)`
ARGV = `Array.new(ARGC_UNSAFE - 1) do |i| String.new(ARGV_UNSAFE[1 + i]) end`
PROGRAM_NAME = `String.new(ARGV_UNSAFE.value)`
STDERR = `(IO::FileDescriptor.from_stdio(2)).tap do |f| f.flush_on_newline = true end`
STDIN = `IO::FileDescriptor.from_stdio(0)`
STDOUT = `(IO::FileDescriptor.from_stdio(1)).tap do |f| f.flush_on_newline = true end`

## Method Summary

- `(command) : String

  Returns the standard output of executing command in a subshell.

- abort(message, status = 1) : NoReturn

  Terminates execution immediately, printing message to `STDERR` and then calling `exit(status)`.

- at_exit(&handler : Int32, Exception? -> ) : Nil

  Registers the given `Proc` for execution when the program exits.

- caller
- delay(delay, &block : -> _)

  Spawns a `Fiber` to compute &block in the background after delay has elapsed.

- exit(status = 0) : NoReturn

  Terminates execution immediately, returning the given status code to the invoking environment.

- fork

  See also: `Process.fork`

- fork(&block)

  See also: `Process.fork`

- future(&exp : -> _)

  Spawns a `Fiber` to compute &block in the background.

- gets(*args, **options)

  Reads a line from `STDIN`.

- lazy(&block : -> _)

  Conditionally spawns a `Fiber` to run &block in the background.

- loop(&block)

  Repeatedly executes the block.

- main(argc : Int32, argv : Pointer(Pointer(UInt8)))

  Main function that acts as C's main function.

- p

  Inspects objects to `STDOUT`, followed by a newline.

- p(object)

  Inspects object to `STDOUT` followed by a newline.

- p(*objects)

  Inspects each object in objects to `STDOUT`, followed by a newline.

- pp(*objects)

  Pretty prints each object in objects to `STDOUT`, followed by a newline.

- pp

  Pretty prints objects to `STDOUT`, followed by a newline.

- pp(object)

  Pretty prints object to `STDOUT` followed by a newline.

- print(*objects : _) : Nil

  Prints objects to STDOUT and then invokes `STDOUT.flush`.

- printf(format_string, *args) : Nil

  Prints a formatted string to `STDOUT`.

- printf(format_string, args : Array | Tuple) : Nil

  Prints a formatted string to `STDOUT`.

- puts(*objects) : Nil

  Prints objects to `STDOUT`, each followed by a newline.

- raise(exception : Exception) : NoReturn

  Raises the exception.

- raise(message : String) : NoReturn

  Raises an Exception with the message.

- rand(x)

  See `Random#rand(x)`.

- rand

  See `Random#rand`.

- read_line(*args, **options)

  Reads a line from `STDIN`.

- sleep

  Blocks the current fiber forever.

- sleep(time : Time::Span)

  Blocks the current Fiber for the specified time span.

- sleep(seconds : Number)

  Blocks the current fiber for the specified number of seconds.

- spawn(*, name : String? = nil, &block)

  Spawns a new fiber.

- sprintf(format_string, *args) : String

  Returns a formatted string.

- sprintf(format_string, args : Array | Tuple) : String

  Returns a formatted string.

- system(command : String, args = nil) : Bool

  Executes the given command in a subshell.

- with_color(color : Symbol)
- with_color

## Macro Summary

- assert_responds_to(var, method)
- debugger
- p!(*exps)

  Prints a series of expressions together with their inspected values.

- parallel(*jobs)

  Runs the commands passed as arguments concurrently (in Fibers) and waits for them to finish.

- pp!(*exps)

  Prints a series of expressions together with their pretty printed values.

- record(name, *properties)

  Defines a `Struct` with the given name and properties.

- spawn(call, *, name = nil)

  Spawns a fiber by first creating a `Proc`, passing the call's expressions to it, and letting the `Proc` finally invoke the call.

### Instance methods inherited from module `Spec::Methods`

assert(file = __FILE__, line = __LINE__, end_line = __END_LINE__, &block) assert, context(description, file = __FILE__, line = __LINE__, &block) context, describe(description, file = __FILE__, line = __LINE__, &block) describe, fail(msg, file = __FILE__, line = __LINE__) fail, it(description = "assert", file = __FILE__, line = __LINE__, end_line = __END_LINE__, &block) it, pending(description = "assert", file = __FILE__, line = __LINE__, end_line = __END_LINE__, &block) pending

### Instance methods inherited from module `Spec::Expectations`

be(value)
be be, be_close(expected, delta) be_close, be_false be_false, be_falsey be_falsey, be_nil be_nil, be_true be_true, be_truthy be_truthy, contain(expected) contain, end_with(expected) end_with, eq(value) eq, expect_raises(klass : T.class, message = nil, file = __FILE__, line = __LINE__, &block) forall T expect_raises, match(value) match, start_with(expected) start_with

## Method Detail

def `(command) : String #

Returns the standard output of executing command in a subshell. Standard input, and error are inherited. The special `$?` variable is set to a `Process::Status` associated with this execution.

Example:

    `echo hi` # => "hi\n"

def abort(message, status = 1) : NoReturn #

Terminates execution immediately, printing message to `STDERR` and then calling `exit(status)`.

def at_exit(&handler : Int32, Exception? -> ) : Nil #

Registers the given `Proc` for execution when the program exits. If multiple handlers are registered, they are executed in reverse order of registration.

    def do_at_exit(str1)
      at_exit { print str1 }
    end

    at_exit { puts "cruel world" }
    do_at_exit("goodbye ")
    exit

Produces:

    goodbye cruel world

The exit status code that will be returned by this program is passed to the block as its first argument. In case of any unhandled exception, it is passed as the second argument to the block, if the program terminates normally or `exit(status)` is called explicitly, then the second argument will be nil.

def caller #
def delay(delay, &block : -> _) #

Spawns a `Fiber` to compute &block in the background after delay has elapsed. Access to get is synchronized between fibers. &block is only called once. May be canceled before &block is called by calling `cancel`.

    d = delay(1) { Process.kill(Signal::KILL, Process.pid) }
    # ... long operations ...
    d.cancel

def exit(status = 0) : NoReturn #

Terminates execution immediately, returning the given status code to the invoking environment.

Registered `at_exit` procs are executed.

def fork #

See also: `Process.fork`

def fork(&block) #

See also: `Process.fork`

def future(&exp : -> _) #

Spawns a `Fiber` to compute &block in the background. Access to get is synchronized between fibers. &block is only called once.

    f = future { `echo hello` }
    # ... other actions ...
    f.get # => "hello\n"

def gets(*args, **options) #

Reads a line from `STDIN`.

See also: `IO#gets`.

def lazy(&block : -> _) #

Conditionally spawns a `Fiber` to run &block in the background. Access to get is synchronized between fibers. &block is only called once. &block doesn't run by default, only when `get` is called.

    l = lazy { expensive_computation }
    spawn { maybe_use_computation(l) }
    spawn { maybe_use_computation(l) }

def loop(&block) #

Repeatedly executes the block.

    loop do
      line = gets
      break unless line
      # ...
    end

def main(argc : Int32, argv : Pointer(Pointer(UInt8))) #

Main function that acts as C's main function. Invokes `Crystal.main`.

Can be redefined. See `Crystal.main` for examples.

def p #

Inspects objects to `STDOUT`, followed by a newline. Returns objects.

    p foo: 23, bar: 42 # => {foo: 23, bar: 42}

See `Object#inspect(io)`

def p(object) #

Inspects object to `STDOUT` followed by a newline. Returns object.

See also: `Object#inspect(io)`.

def p(*objects) #

Inspects each object in objects to `STDOUT`, followed by a newline. Returns objects.

See also: `Object#inspect(io)`.

def pp(*objects) #

Pretty prints each object in objects to `STDOUT`, followed by a newline. Returns objects.

See also: `Object#pretty_print(pp)`.

def pp #

Pretty prints objects to `STDOUT`, followed by a newline. Returns objects.

    p foo: 23, bar: 42 # => {foo: 23, bar: 42}

See `Object#pretty_print(pp)`

def pp(object) #

Pretty prints object to `STDOUT` followed by a newline. Returns object.

See also: `Object#pretty_print(pp)`.

def print(*objects : _) : Nil #

Prints objects to STDOUT and then invokes `STDOUT.flush`.

See also: `IO#print`.

def printf(format_string, *args) : Nil #

Prints a formatted string to `STDOUT`.

For details on the format string, see `sprintf`.

def printf(format_string, args : Array | Tuple) : Nil #

Prints a formatted string to `STDOUT`.

For details on the format string, see `sprintf`.

def puts(*objects) : Nil #

Prints objects to `STDOUT`, each followed by a newline.

See also: `IO#puts`.

def raise(exception : Exception) : NoReturn #

Raises the exception.

This will set the exception's callstack if it hasn't been already. Re-raising a previously catched exception won't replace the callstack.

def raise(message : String) : NoReturn #

Raises an Exception with the message.

def rand(x) #

See `Random#rand(x)`.

def rand #

See `Random#rand`.

def read_line(*args, **options) #

Reads a line from `STDIN`.

See also: `IO#read_line`.

def sleep #

Blocks the current fiber forever.

Meanwhile, other ready-to-execute fibers might start their execution.

def sleep(time : Time::Span) #

Blocks the current Fiber for the specified time span.

While this fiber is waiting this time other ready-to-execute fibers might start their execution.

def sleep(seconds : Number) #

Blocks the current fiber for the specified number of seconds.

While this fiber is waiting this time other ready-to-execute fibers might start their execution.

def spawn(*, name : String? = nil, &block) #

Spawns a new fiber.

The newly created fiber doesn't run as soon as spawned.

Example:

    # Write "1" every 1 second and "2" every 2 seconds for 6 seconds.

    ch = Channel(Nil).new

    spawn do
      6.times do
        sleep 1
        puts 1
      end
      ch.send(nil)
    end

    spawn do
      3.times do
        sleep 2
        puts 2
      end
      ch.send(nil)
    end

    2.times { ch.receive }

def sprintf(format_string, *args) : String #

Returns a formatted string. The string is produced according to the format_string with format specifiers being replaced by values from args formatted according to the specifier.

Within the format string, any characters other than format specifiers (specifiers beginning with `%`) are copied to the result.

The syntax for a format specifier is:

    %[flags][width][.precision]type

A format specifier consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character.

The field type controls how the corresponding `sprintf` argument is to be interpreted, while the flags modify that interpretation.

The field type characters are:

        Field |  Integer Format
        ------+--------------------------------------------------------------
          b   | Formats argument as a binary number.
          d   | Formats argument as a decimal number.
          i   | Same as d.
          o   | Formats argument as an octal number.
          x   | Formats argument as a hexadecimal number using lowercase letters.
          X   | Same as x, but uses uppercase letters.

        Field |  Float Format
        ------+--------------------------------------------------------------
          e   | Formats floating point argument into exponential notation
              | with one digit before the decimal point as [-]d.dddddde[+-]dd.
              | The precision specifies the number of digits after the decimal
              | point (defaulting to six).
          E   | Equivalent to e, but uses an uppercase E to indicate
              | the exponent.
          f   | Formats floating point argument as [-]ddd.dddddd,
              | where the precision specifies the number of digits after
              | the decimal point.
          g   | Formats a floating point number using exponential form
              | if the exponent is less than -4 or greater than or
              | equal to the precision, or in dd.dddd form otherwise.
              | The precision specifies the number of significant digits.
          G   | Equivalent to g, but use an uppercase E in exponent form.
          a   | Formats floating point argument as [-]0xh.hhhhp[+-]dd,
              | which is consisted from optional sign, "0x", fraction part
              | as hexadecimal, "p", and exponential part as decimal.
          A   | Equivalent to a, but use uppercase X and P.

        Field |  Other Format
        ------+--------------------------------------------------------------
          c   | Argument is the numeric code for a single character or
              | a single character string itself.
          s   | Argument is a string to be substituted.  If the format
              | sequence contains a precision, at most that many characters
              | will be copied.
          %   | A percent sign itself will be displayed.  No argument taken.

The flags modifies the behavior of the formats. The flag characters are:

      Flag     | Applies to    | Meaning
      ---------+---------------+-----------------------------------------
      space    | bdiouxX       | Add a leading space character to
               | aAeEfgG       | non-negative numbers.
               | (numeric fmt) | For o, x, X, b, use
               |               | a minus sign with absolute value for
               |               | negative values.
      ---------+---------------+-----------------------------------------
      +        | bdiouxX       | Add a leading plus sign to non-negative
               | aAeEfgG       | numbers.
               | (numeric fmt) | For o, x, X, b, use
               |               | a minus sign with absolute value for
               |               | negative values.
      ---------+---------------+-----------------------------------------
      -        | all           | Left-justify the result of this conversion.
      ---------+---------------+-----------------------------------------
      0 (zero) | bdiouxX       | Pad with zeros, not spaces.
               | aAeEfgG       | For o, x, X, b, radix-1
               | (numeric fmt) | is used for negative numbers formatted as
               |               | complements.

Examples of flags:

Decimal number conversion

    sprintf "%d", 123  # => "123"
    sprintf "%+d", 123 # => "+123"
    sprintf "% d", 123 # => " 123"

Octal number conversion

    sprintf "%o", 123   # => "173"
    sprintf "%+o", 123  # => "+173"
    sprintf "%o", -123  # => "-173"
    sprintf "%+o", -123 # => "-173"

Hexadecimal number conversion

    sprintf "%x", 123   # => "7b"
    sprintf "%+x", 123  # => "+7b"
    sprintf "%x", -123  # => "-7b"
    sprintf "%+x", -123 # => "-7b"
    sprintf "%#x", 0    # => "0"
    sprintf "% x", 123  # => " 7b"
    sprintf "% x", -123 # => "-7b"
    sprintf "%X", 123   # => "7B"
    sprintf "%#X", -123 # => "-7B"

Binary number conversion

    sprintf "%b", 123    # => "1111011"
    sprintf "%+b", 123   # => "+1111011"
    sprintf "%+b", -123  # => "-1111011"
    sprintf "%b", -123   # => "-1111011"
    sprintf "%#b", 0     # => "0"
    sprintf "% b", 123   # => " 1111011"
    sprintf "%+ b", 123  # => "+ 1111011"
    sprintf "% b", -123  # => "-1111011"
    sprintf "%+ b", -123 # => "-1111011"

Floating point conversion

    sprintf "%a", 123 # => "0x1.ecp+6"
    sprintf "%A", 123 # => "0X1.ECP+6"

Exponential form conversion

    sprintf "%g", 123.4          # => "123.4"
    sprintf "%g", 123.4567       # => "123.457"
    sprintf "%20.8g", 1234.56789 # => "           1234.5679"
    sprintf "%20.8g", 123456789  # => "       1.2345679e+08"
    sprintf "%20.8G", 123456789  # => "       1.2345679E+08"
    sprintf "%20.8g", -123456789 # => "       -1.2345679e+08"
    sprintf "%20.8G", -123456789 # => "       -1.2345679E+08"

The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field.

Examples of width:

    sprintf "%20d", 123   # => "                 123"
    sprintf "%+20d", 123  # => "                +123"
    sprintf "%020d", 123  # => "00000000000000000123"
    sprintf "%+020d", 12  # => "+0000000000000000123"
    sprintf "% 020d", 123 # => " 0000000000000000123"
    sprintf "%-20d", 123  # => "123                 "
    sprintf "%-+20d", 123 # => "+123                "
    sprintf "%- 20d", 123 # => " 123                "
    sprintf "%020x", -123 # => "00000000000000000-7b"
    sprintf "%020X", -123 # => "00000000000000000-7B"

For numeric fields, the precision controls the number of decimal places displayed.

For string fields, the precision determines the maximum number of characters to be copied from the string.

Examples of precisions:

Precision for `d`, `o`, `x` and `b` is minimum number of digits

    sprintf "%20.8d", 123   # => "                 123"
    sprintf "%020.8d", 123  # => "00000000000000000123"
    sprintf "%20.8o", 123   # => "                 173"
    sprintf "%020.8o", 123  # => "00000000000000000173"
    sprintf "%20.8x", 123   # => "                  7b"
    sprintf "%020.8x", 123  # => "0000000000000000007b"
    sprintf "%20.8b", 123   # => "            01111011"
    sprintf "%20.8d", -123  # => "                -123"
    sprintf "%020.8d", -123 # => "0000000000000000-123"
    sprintf "%20.8o", -123  # => "                -173"
    sprintf "%20.8x", -123  # => "                 -7b"
    sprintf "%20.8b", -11   # => "               -1011"

Precision for `e` is number of digits after the decimal point.

    sprintf "%20.8e", 1234.56789 # => "      1.23456789e+03"

Precision for `f` is number of digits after the decimal point.

    sprintf "%20.8f", 1234.56789 # => "       1234.56789000"

Precision for `g` is number of significant digits.

    sprintf "%20.8g", 1234.56789 # => "           1234.5679"
    sprintf "%20.8g", 123456789  # => "       1.2345679e+08"
    sprintf "%-20.8g", 123456789 # => "1.2345679e+08       "

Precision for `s` is maximum number of characters.

    sprintf "%20.8s", "string test" # => "            string t"

Additional examples:

    sprintf "%d %04x", 123, 123             # => "123 007b"
    sprintf "%08b '%4s'", 123, 123          # => "01111011 ' 123'"
    sprintf "%+g:% g:%-g", 1.23, 1.23, 1.23 # => "+1.23: 1.23:1.23"

def sprintf(format_string, args : Array | Tuple) : String #

Returns a formatted string. The string is produced according to the format_string with format specifiers being replaced by values from args formatted according to the specifier.

Within the format string, any characters other than format specifiers (specifiers beginning with `%`) are copied to the result.

The syntax for a format specifier is:

    %[flags][width][.precision]type

A format specifier consists of a percent sign, followed by optional flags, width, and precision indicators, then terminated with a field type character.

The field type controls how the corresponding `sprintf` argument is to be interpreted, while the flags modify that interpretation.

The field type characters are:

        Field |  Integer Format
        ------+--------------------------------------------------------------
          b   | Formats argument as a binary number.
          d   | Formats argument as a decimal number.
          i   | Same as d.
          o   | Formats argument as an octal number.
          x   | Formats argument as a hexadecimal number using lowercase letters.
          X   | Same as x, but uses uppercase letters.

        Field |  Float Format
        ------+--------------------------------------------------------------
          e   | Formats floating point argument into exponential notation
              | with one digit before the decimal point as [-]d.dddddde[+-]dd.
              | The precision specifies the number of digits after the decimal
              | point (defaulting to six).
          E   | Equivalent to e, but uses an uppercase E to indicate
              | the exponent.
          f   | Formats floating point argument as [-]ddd.dddddd,
              | where the precision specifies the number of digits after
              | the decimal point.
          g   | Formats a floating point number using exponential form
              | if the exponent is less than -4 or greater than or
              | equal to the precision, or in dd.dddd form otherwise.
              | The precision specifies the number of significant digits.
          G   | Equivalent to g, but use an uppercase E in exponent form.
          a   | Formats floating point argument as [-]0xh.hhhhp[+-]dd,
              | which is consisted from optional sign, "0x", fraction part
              | as hexadecimal, "p", and exponential part as decimal.
          A   | Equivalent to a, but use uppercase X and P.

        Field |  Other Format
        ------+--------------------------------------------------------------
          c   | Argument is the numeric code for a single character or
              | a single character string itself.
          s   | Argument is a string to be substituted.  If the format
              | sequence contains a precision, at most that many characters
              | will be copied.
          %   | A percent sign itself will be displayed.  No argument taken.

The flags modifies the behavior of the formats. The flag characters are:

      Flag     | Applies to    | Meaning
      ---------+---------------+-----------------------------------------
      space    | bdiouxX       | Add a leading space character to
               | aAeEfgG       | non-negative numbers.
               | (numeric fmt) | For o, x, X, b, use
               |               | a minus sign with absolute value for
               |               | negative values.
      ---------+---------------+-----------------------------------------
      +        | bdiouxX       | Add a leading plus sign to non-negative
               | aAeEfgG       | numbers.
               | (numeric fmt) | For o, x, X, b, use
               |               | a minus sign with absolute value for
               |               | negative values.
      ---------+---------------+-----------------------------------------
      -        | all           | Left-justify the result of this conversion.
      ---------+---------------+-----------------------------------------
      0 (zero) | bdiouxX       | Pad with zeros, not spaces.
               | aAeEfgG       | For o, x, X, b, radix-1
               | (numeric fmt) | is used for negative numbers formatted as
               |               | complements.

Examples of flags:

Decimal number conversion

    sprintf "%d", 123  # => "123"
    sprintf "%+d", 123 # => "+123"
    sprintf "% d", 123 # => " 123"

Octal number conversion

    sprintf "%o", 123   # => "173"
    sprintf "%+o", 123  # => "+173"
    sprintf "%o", -123  # => "-173"
    sprintf "%+o", -123 # => "-173"

Hexadecimal number conversion

    sprintf "%x", 123   # => "7b"
    sprintf "%+x", 123  # => "+7b"
    sprintf "%x", -123  # => "-7b"
    sprintf "%+x", -123 # => "-7b"
    sprintf "%#x", 0    # => "0"
    sprintf "% x", 123  # => " 7b"
    sprintf "% x", -123 # => "-7b"
    sprintf "%X", 123   # => "7B"
    sprintf "%#X", -123 # => "-7B"

Binary number conversion

    sprintf "%b", 123    # => "1111011"
    sprintf "%+b", 123   # => "+1111011"
    sprintf "%+b", -123  # => "-1111011"
    sprintf "%b", -123   # => "-1111011"
    sprintf "%#b", 0     # => "0"
    sprintf "% b", 123   # => " 1111011"
    sprintf "%+ b", 123  # => "+ 1111011"
    sprintf "% b", -123  # => "-1111011"
    sprintf "%+ b", -123 # => "-1111011"

Floating point conversion

    sprintf "%a", 123 # => "0x1.ecp+6"
    sprintf "%A", 123 # => "0X1.ECP+6"

Exponential form conversion

    sprintf "%g", 123.4          # => "123.4"
    sprintf "%g", 123.4567       # => "123.457"
    sprintf "%20.8g", 1234.56789 # => "           1234.5679"
    sprintf "%20.8g", 123456789  # => "       1.2345679e+08"
    sprintf "%20.8G", 123456789  # => "       1.2345679E+08"
    sprintf "%20.8g", -123456789 # => "       -1.2345679e+08"
    sprintf "%20.8G", -123456789 # => "       -1.2345679E+08"

The field width is an optional integer, followed optionally by a period and a precision. The width specifies the minimum number of characters that will be written to the result for this field.

Examples of width:

    sprintf "%20d", 123   # => "                 123"
    sprintf "%+20d", 123  # => "                +123"
    sprintf "%020d", 123  # => "00000000000000000123"
    sprintf "%+020d", 12  # => "+0000000000000000123"
    sprintf "% 020d", 123 # => " 0000000000000000123"
    sprintf "%-20d", 123  # => "123                 "
    sprintf "%-+20d", 123 # => "+123                "
    sprintf "%- 20d", 123 # => " 123                "
    sprintf "%020x", -123 # => "00000000000000000-7b"
    sprintf "%020X", -123 # => "00000000000000000-7B"

For numeric fields, the precision controls the number of decimal places displayed.

For string fields, the precision determines the maximum number of characters to be copied from the string.

Examples of precisions:

Precision for `d`, `o`, `x` and `b` is minimum number of digits

    sprintf "%20.8d", 123   # => "                 123"
    sprintf "%020.8d", 123  # => "00000000000000000123"
    sprintf "%20.8o", 123   # => "                 173"
    sprintf "%020.8o", 123  # => "00000000000000000173"
    sprintf "%20.8x", 123   # => "                  7b"
    sprintf "%020.8x", 123  # => "0000000000000000007b"
    sprintf "%20.8b", 123   # => "            01111011"
    sprintf "%20.8d", -123  # => "                -123"
    sprintf "%020.8d", -123 # => "0000000000000000-123"
    sprintf "%20.8o", -123  # => "                -173"
    sprintf "%20.8x", -123  # => "                 -7b"
    sprintf "%20.8b", -11   # => "               -1011"

Precision for `e` is number of digits after the decimal point.

    sprintf "%20.8e", 1234.56789 # => "      1.23456789e+03"

Precision for `f` is number of digits after the decimal point.

    sprintf "%20.8f", 1234.56789 # => "       1234.56789000"

Precision for `g` is number of significant digits.

    sprintf "%20.8g", 1234.56789 # => "           1234.5679"
    sprintf "%20.8g", 123456789  # => "       1.2345679e+08"
    sprintf "%-20.8g", 123456789 # => "1.2345679e+08       "

Precision for `s` is maximum number of characters.

    sprintf "%20.8s", "string test" # => "            string t"

Additional examples:

    sprintf "%d %04x", 123, 123             # => "123 007b"
    sprintf "%08b '%4s'", 123, 123          # => "01111011 ' 123'"
    sprintf "%+g:% g:%-g", 1.23, 1.23, 1.23 # => "+1.23: 1.23:1.23"

def system(command : String, args = nil) : Bool #

Executes the given command in a subshell. Standard input, output and error are inherited. Returns `true` if the command gives zero exit code, `false` otherwise. The special `$?` variable is set to a `Process::Status` associated with this execution.

If command contains no spaces and args is given, it will become its argument list.

If command contains spaces and args is given, command must include `"${@}"` (including the quotes) to receive the argument list.

No shell interpretation is done in args.

Example:

    system("echo *")

Produces:

    LICENSE shard.yml Readme.md spec src

def with_color(color : Symbol) #
def with_color #

## Macro Detail

macro assert_responds_to(var, method) #
macro debugger #
macro p!(*exps) #

Prints a series of expressions together with their inspected values. Useful for print style debugging.

    a = 1
    p! a # => "a # => 1"

    p! [1, 2, 3].map(&.to_s) # => "[1, 2, 3].map(&.to_s) # => ["1", "2", "3"]"

See also: `p`, `Object#inspect`.

macro parallel(*jobs) #

Runs the commands passed as arguments concurrently (in Fibers) and waits for them to finish.

    def say(word)
      puts word
    end

    # Will print out the three words concurrently
    parallel(
      say("concurrency"),
      say("is"),
      say("easy")
    )

Can also be used to conveniently collect the return values of the concurrent operations.

    def concurrent_job(word)
      word
    end

    a, b, c =
      parallel(
        concurrent_job("concurrency"),
        concurrent_job("is"),
        concurrent_job("easy")
      )

    a # => "concurrency"
    b # => "is"
    c # => "easy"

Due to the concurrent nature of this macro, it is highly recommended to handle any exceptions within the concurrent calls. Unhandled exceptions raised within the concurrent operations will be re-raised inside the parent fiber as `ConcurrentExecutionException`, with the `cause` attribute set to the original exception.

macro pp!(*exps) #

Prints a series of expressions together with their pretty printed values. Useful for print style debugging.

    a = 1
    pp! a # => "a # => 1"

    pp! [1, 2, 3].map(&.to_s) # => "[1, 2, 3].map(&.to_s) # => ["1", "2", "3"]"

See also: `pp`, `Object#pretty_inspect`.

macro record(name, *properties) #

Defines a `Struct` with the given name and properties.

The generated struct has a constructor with the given properties in the same order as declared. The struct only provides getters, not setters, making it immutable by default.

The properties can be type declarations or assignments.

You can pass a block to this macro, that will be inserted inside the struct definition.

    record Point, x : Int32, y : Int32

    Point.new 1, 2 # => #<Point(@x=1, @y=2)>

An example with the block version:

    record Person, first_name : String, last_name : String do
      def full_name
        "#{first_name} #{last_name}"
      end
    end

    person = Person.new "John", "Doe"
    person.full_name # => "John Doe"

An example with type declarations and default values:

    record Point, x : Int32 = 0, y : Int32 = 0

    Point.new      # => #<Point(@x=0, @y=0)>
    Point.new y: 2 # => #<Point(@x=0, @y=2)>

An example with assignments (in this case the compiler must be able to infer the types from the default values):

    record Point, x = 0, y = 0

    Point.new      # => #<Point(@x=0, @y=0)>
    Point.new y: 2 # => #<Point(@x=0, @y=2)>

This macro also provides a `copy_with` method which returns a copy of the record with the provided properties altered.

    record Point, x = 0, y = 0

    p = Point.new y: 2 # => #<Point(@x=0, @y=2)>
    p.copy_with x: 3   # => #<Point(@x=3, @y=2)>
    p                  # => #<Point(@x=0, @y=2)>

macro spawn(call, *, name = nil) #

Spawns a fiber by first creating a `Proc`, passing the call's expressions to it, and letting the `Proc` finally invoke the call.

Compare this:

    i = 0
    while i < 5
      spawn { print(i) }
      i += 1
    end
    Fiber.yield
    # Output: 55555

To this:

    i = 0
    while i < 5
      spawn print(i)
      i += 1
    end
    Fiber.yield
    # Output: 01234

This is because in the first case all spawned fibers refer to the same local variable, while in the second example copies of i are passed to a `Proc` that eventually invokes the call.