TARGET_GENEX_EVAL

This generator expression belongs to the Multi-level Expression Evaluation family. See that section for related generator expressions.

Syntax

$<TARGET_GENEX_EVAL:tgt,expr>

Added in version 3.12.

Content of expr evaluated as a generator expression in the context of tgt target. This enables consumption of custom target properties that themselves contain generator expressions.

Having the capability to evaluate generator expressions is very useful when you want to manage custom properties supporting generator expressions. For example:

add_library(foo ...)

set_property(TARGET foo PROPERTY
  CUSTOM_KEYS $<$<CONFIG:DEBUG>:FOO_EXTRA_THINGS>
)

add_custom_target(printFooKeys
  COMMAND ${CMAKE_COMMAND} -E echo $<TARGET_PROPERTY:foo,CUSTOM_KEYS>
)

This naive implementation of the printFooKeys custom command is wrong because CUSTOM_KEYS target property is not evaluated and the content is passed as is (i.e. $<$<CONFIG:DEBUG>:FOO_EXTRA_THINGS>).

To have the expected result (i.e. FOO_EXTRA_THINGS if config is Debug), it is required to evaluate the output of $<TARGET_PROPERTY:foo,CUSTOM_KEYS>:

add_custom_target(printFooKeys
  COMMAND ${CMAKE_COMMAND} -E
    echo $<TARGET_GENEX_EVAL:foo,$<TARGET_PROPERTY:foo,CUSTOM_KEYS>>
)