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z_vcpkg_forward_output_variable.md

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z_vcpkg_forward_output_variable

The latest version of this document lives in the vcpkg repo.

This macro helps with forwarding values from inner function calls, through a local function scope, into pointer out parameters.

z_vcpkg_forward_output_variable(ptr_to_parent_var var_to_forward)

is equivalent to

if(DEFINED ptr_to_parent_var)
    if(DEFINED value_var)
        set("${ptr_to_parent_var}" "${value_var}" PARENT_SCOPE)
    else()
        unset("${ptr_to_parent_var}" PARENT_SCOPE)
    endif()
endif()

Take note that the first argument should be a local variable that has a value of the parent variable name. Most commonly, this local is the result of a pointer-out parameter to a function. If the variable in the first parameter is not defined, this function does nothing, simplifying functions with optional out parameters. Most commonly, this should be used in cases like:

function(my_function out_var)
    file(SHA512 "somefile.txt" local_var)
    z_vcpkg_forward_output_variable(out_var local_var)
endfunction()

Source

scripts/cmake/z_vcpkg_forward_output_variable.cmake