Built-in predicates¶

A predicate is a trailing path segment ending with a question mark (?). A predicate "queries" the value obtained by resolving preceding path segments and returns true or false.

Note that a question mark (?) is not a valid identifier character. If a variable or property contains a literal ?, bracket notation must be used: foo["bar?"].

array?¶

Resolves to true if the value is an array, or false otherwise.

{%- assign
  x = [1, 2, 3],
  y = "foo",
  z = null,
-%}

{{ x.array? }}
{{ y.array? }}
{{ z.array? }}

Output

true
false
false

blank?¶

Resolves to true if the value is null, a string containing only whitespace, or an empty string, array or hash.

{%- assign
  x = "    \n    \t",
  y = "foo",
  z = [],
-%}

{{ x.blank? }}
{{ y.blank? }}
{{ z.blank? }}

Output

true
false
true

defined?¶

Resolves to true if the value is the the special result Nothing. Undefined variables resolve to Nothing, as do math expressions that can't produce a numeric value.

{%- assign
  x = null,
  y = nosuchthing,
  z = {},
-%}

{{ x.defined? }}
{{ y.defined? }}
{{ z.foo.defined? }}

Output

true
false
false

empty?¶

Resolves to true if the value is null or an empty string, array or hash.

{%- assign
  x = "    \n    \t",
  y = "",
  z = [],
-%}

{{ x.empty? }}
{{ y.empty? }}
{{ z.empty? }}

Output

false
true
true

number?¶

Resolves to true if the value is a number type.

{%- assign
  x = 1,
  y = 2.3,
  z = "42",
-%}

{{ x.number? }}
{{ y.number? }}
{{ z.number? }}

Output

true
true
false

numeric?¶

Resolves to true if the value is a number type or can be coerced to a number.

{%- assign
  x = null,
  y = 2.3,
  z = "42",
-%}

{{ x.numeric? }}
{{ y.numeric? }}
{{ z.numeric? }}

Output

false
true
true

object?¶

Resolves to true if the value is an object (aka hash, dictionary or mapping).

{%- assign
  x = 42,
  y = {"a": 1},
  z = [1,2,3],
-%}

{{ x.object? }}
{{ y.object? }}
{{ z.object? }}

Output

false
true
false

string?¶

Resolves to true if the value is a string type.

{%- assign
  x = "foo",
  y = "42",
  z = [1,2,3],
-%}

{{ x.string? }}
{{ y.string? }}
{{ z.string? }}

Output

true
true
false

null?¶

Resolves to true if the value is null.

{%- assign
  x = null,
  y = nosuchthing,
  z = {"foo": null},
-%}

{{ x.null? }}
{{ y.null? }}
{{ z.foo.null? }}

Output

true
false
true