kex docs Standard Library

Truthyable

trait Truthyable

Truthyable: what counts as true when a value is used as a condition.

The rule is Crystal's, and it is short: only false, None and () are falsy. Everything else is truthy, including 0, "" and [], which some languages treat as false and Kex deliberately does not.

0.truthy?       # => true
"".truthy?      # => true
[].truthy?      # => true
None.truthy?    # => false
false.truthy?   # => false

When you want the "is there anything here" question instead, that is Blankable's blank? / present?.

There is no NaN to consider: a float operation that would produce one raises instead, matching BEAM (see nonFiniteFloatError in src/interpreter/value.cxx).

Implemented by Bool, Integer, Float, String, Optional<X>, [X], Map<K, V>.

Required functions

An implementor writes these.

truthy?

truthy? : Bool

Returns true when the value counts as true in a condition.

Returns true unless the value is false, None or ()

Examples
1.truthy?        # => true
None.truthy?     # => false

type Bool

Implements Blankable, Truthyable.

truthy? Truthyable

truthy? : Bool

Returns the boolean itself.

Returns the value

Examples
true.truthy?    # => true
false.truthy?   # => false

not

not : Bool

Returns the negation of this boolean.

!flag says the same thing, and is the spelling to reach for when the value is already to hand. This one exists for the position ! cannot take: the end of a chain, where what is being negated is whatever the chain just produced. falsy? answers the same question for any Truthyable value; not is the one that both takes and answers a Bool.

Returns false for true, and true for false

Examples
true.not    # => false
false.not   # => true

At the end of a chain

book.borrowed?.not

Defined in other modules

Blankable
blank?

extends Integer

More functions for Integer, added by this module.

Implements Truthyable.

truthy? Truthyable

truthy? : Bool

Always true, including for zero.

Zero is a number, not an absence. Compare it explicitly when zero means something: count == 0.

Returns always true

Examples
0.truthy?    # => true
42.truthy?   # => true

extends Float

More functions for Float, added by this module.

Implements Truthyable.

truthy? Truthyable

truthy? : Bool

Always true, including for zero.

Returns always true

Examples
0.0.truthy?   # => true

extends String

More functions for String, added by this module.

Implements Truthyable.

truthy? Truthyable

truthy? : Bool

Always true, including for the empty string.

Use blank? from Blankable when an empty or whitespace-only string should count as nothing.

Returns always true

Examples
"".truthy?      # => true
"".blank?       # => true   (the question usually meant)

extends Optional<X>

More functions for Optional, added by this module.

Implements Truthyable.

truthy? Truthyable

truthy? : Bool

Returns true for a Just and false for None.

The one type where truthiness is genuinely about presence, which is what makes an optional usable directly as a condition.

Returns true when a value is present

Examples
Just(0).truthy?    # => true
None.truthy?       # => false

extends [X]

More functions for List, added by this module.

Implements Truthyable.

truthy? Truthyable

truthy? : Bool

Always true, including for the empty list.

Use empty? or blank? when an empty list should count as nothing.

Returns always true

Examples
[].truthy?   # => true
[].blank?    # => true   (the question usually meant)

extends Map<K, V>

More functions for Map, added by this module.

Implements Truthyable.

truthy? Truthyable

truthy? : Bool

Always true, including for the empty map.

Returns always true

Examples
{}.truthy?   # => true
{}.blank?    # => true   (the question usually meant)