role Real
Error ReportCollection examples

Non-complex number

role Real does Numeric { ... }

Common role for non-Complex numbers.


method Bridge

Defined as:

method Bridge(Real:D:)

Default implementation coerces the invocant to Num and that's the behavior of this method in core Real types. This method primarily exist to make it easy to implement custom Real types by users, with the Bridge method returning one of the core Real types (NOT necessarily a Num) that best represent the custom Real type. In turn, this lets all the core operators and methods obtain a usable value they can work with.

As an example, we can implement a custom Temperature type. It has a unit of measure and the value, which are given during instantiation. We can implement custom operators or conversion methods that work with this type. When it comes to regular mathematical operators, however, we can simply use the .Bridge method to convert the Temperature to Kelvin expressed in one of the core numeric types:

class Temperature is Real {
    has Str:D  $.unit  is required where any <K F C>;
    has Real:D $.value is required;
    method new ($value:$unit = 'K'{ self.bless :$value :$unit }
    # Note: implementing .new() that handles $value of type Temperature is left as an exercise 
    method Bridge {
        when $!unit eq 'F' { ($!value + 459.67) × 5/9 }
        when $!unit eq 'C' {  $!value + 273.15 }
    method gist { self.Str }
    method Str  { "$!value degrees $!unit" }
sub postfix:<> { Temperature.new: $^value:unit<C> }
sub postfix:<> { Temperature.new: $^value:unit<F> }
sub postfix:<K> { Temperature.new: $^value:unit<K> }
my $human := 36.6℃;
my $book  := 451℉;
my $sun   := 5778K;
say $human;                # OUTPUT: «36.6 degrees C␤» 
say $human + $book + $sun# OUTPUT: «6593.677777777778␤» 
say 123+ 456K;           # OUTPUT: «579␤»

As we can see from the last two lines of the output, the type of the bridged result is not forced to be any particular core type. It is a Rat, when we instantiated Temperature with a Rat or when conversion was involved, and it is an Int when we instantiated Temperature with an Int.

method Complex

method Complex(Real:D: --> Complex:D)

Converts the number to a Complex with the number converted to a Num as its real part and 0e0 as the imaginary part.

method Rat

method Rat(Real:D: Real $epsilon = 1e-6)

Converts the number to a Rat with the precision $epsilon.

method Real

Defined as:

multi method Real(Real:D: --> Real:D)
multi method Real(Real:U: --> Real:D)

The :D variant simply returns the invocant. The :U variant issues a warning about using an uninitialized value in numeric context and then returns self.new.

routine rand

sub term:<rand> (--> Num:D)
method rand(Real:D: --> Real:D)

Returns a pseudo-random number between zero (inclusive) and the number (non-inclusive). The Bridge method is used to coerce the Real to a numeric that supports rand method.

The term form returns a pseudo-random Num between 0e0 (inclusive) and 1e0 (non-inclusive.)

method sign

method sign(Real:D:)

Returns -1 if the number is negative, 0 if it is zero and 1 otherwise.

method round

method round(Real:D: $scale = 1)

Rounds the number to scale $scale. If $scale is 1, rounds to an integer. If scale is 0.1, rounds to one digit after the radix point (period or comma), etc.

method floor

method floor(Real:D: --> Int:D)

Return the largest integer not greater than the number.

method ceiling

method ceiling(Real:D: --> Int:D)

Returns the smallest integer not less than the number.

method truncate

method truncate(Real:D: --> Int:D)

Rounds the number towards zero.

method polymod

method polymod(Real:D: +@mods)

Returns the remainders after applying sequentially all divisors in the @mods argument; the last element of the array will be the last remainder.

say (1e8+1).polymod(10 xx 8);  # OUTPUT: «(1 0 0 0 0 0 0 0 1)␤»

10 xx 8 is simply an array with eight number 10s; the first division by 10 will return 1 as a remainder, while the rest, up to the last, will return 0. With 8 divisors, as above, the result will have one more elements, in this case for the last remainder.

method base

method base(Real:D: Int:D $base where 2..36$digits? --> Str:D)

Converts the number to a string, using $base as base. For $base larger than ten, capital Latin letters are used.

255.base(16);            # 'FF'

The optional $digits argument asks for that many digits of fraction (which may not be negative). If omitted, a reasonable default is chosen based on type. For Int this default is 0. For Num, the default is 8. For Rational, the number of places is scaled to the size of the denominator, with a minimum of 6.

A special value of Whatever (*) can be given as $digits, which functions the same as when $digits is not specified for all Real types except the Rationals. For Rationals, the Whatever indicates that you wish all of the possible digits of the fractional part, but use caution: since there's no detection of repeating fractional parts (the algorithm will eventually stop after generating 2**63 digits).

The final digit produced is always rounded.

say pi.base(103);      # OUTPUT: «3.142␤» 
say (1/128).base(10*); # OUTPUT: «0.0078125␤» 
say (1/100).base(10*); # OUTPUT: «0.01␤» 
say (1/3)  .base(10*); # WRONG: endlessly repeating fractional part

For reverse operation, see parse-base