How Twig ternary statements work by John Dohm

how-twig-ternary-statements-work.twig

{#
  Ternary Statements: Ternaries evaluate the variable 
  based on whether it is truthful
#}

{{ foo ? 'yes' : 'no' }} {# Returns 'yes' or 'no' #}
{{ foo ?: 'no' }} {# Returns foo or 'no' #}
{{ foo ? 'yes' }} {# Returns 'yes' or nothing #}

{#
  Ternary Statements: Ternaries evaluate the variable 
  based on whether it is truthful
#}

{{ foo ?? 'no' }} {# Returns foo or 'no' #}

{# Difference in variable evaluation #}

{{ '' ?: 'no' }} {# Returns 'no' (because '' is falsey) #}
{{ '' ?? 'no' }} {# Returns '' (because '' is defined and not null) #}

{# Difference in handling undefined variables #}

{{ undefinedVar ?? 'fallback' }} {# Returns 'fallback' #}
{{ undefinedVar | default('fallback') }} {# Returns 'fallback' #}
{{ undefinedVar ?: 'fallback' }} {# Throws 'undefinedVar' does not exist (error)  #}