instance method
Enumerable#one?
() -> bool
() { (Elem) -> ::boolish } -> bool
one? → true or false
one?(pattern) → true or false
one? {|element| ... } → true or false
enum.c
View on GitHub ↗
static VALUE
enum_one(int argc, VALUE *argv, VALUE obj)
{
struct MEMO *memo = MEMO_ENUM_NEW(Qundef);
VALUE result;
WARN_UNUSED_BLOCK(argc);
ENUM_BLOCK_CALL(one);
result = memo->v1;
if (UNDEF_P(result)) return Qfalse;
return result;
}
Returns whether exactly one element meets a given criterion.
With no argument and no block, returns whether exactly one element is truthy:
Example
(1..1).one? # => true [1, nil, false].one? # => true (1..4).one? # => false {foo: 0}.one? # => true {foo: 0, bar: 1}.one? # => false [].one? # => false
With argument pattern and no block, returns whether for exactly one element element, pattern === element:
Example
[nil, false, 0].one?(Integer) # => true [nil, false, 0].one?(Numeric) # => true [nil, false, 0].one?(Float) # => false %w[bar baz bat bam].one?(/m/) # => true %w[bar baz bat bam].one?(/foo/) # => false %w[bar baz bat bam].one?('ba') # => false {foo: 0, bar: 1, baz: 2}.one?(Array) # => false {foo: 0}.one?(Array) # => true [].one?(Integer) # => false
With a block given, returns whether the block returns a truthy value for exactly one element:
Example
(1..4).one? {|element| element < 2 } # => true (1..4).one? {|element| element < 1 } # => false {foo: 0, bar: 1, baz: 2}.one? {|key, value| value < 1 } # => true {foo: 0, bar: 1, baz: 2}.one? {|key, value| value < 2 } # => false