Can't compile with the development solution config


While all of my code compiles fine when the solution config is set to development editor, when I try to switch to development for building the project will no longer compile.
I’m getting the following error:

Error 1 error LNK2019: unresolved external symbol “public: static float __cdecl UMTools::GetSign(float)” (?GetSign@UMTools@@SAMM@Z) referenced in function “private: void __cdecl AMothershipPlayerCharacter::AxisX(float)” (?AxisX@AMothershipPlayerCharacter@@AEAAXM@Z) C:\Users\mbradley\Documents\GitHub\HEngine_UnrealVRDemo\Intermediate\ProjectFiles\MothershipPlayerCharacter.cpp.obj MothershipDemo

The MTools class is a blueprint function library.
If anyone has ideas of what to try to resolve this, it would be much appreciated!

Are there any #ifdef blocks around your UMTools::GetSign declaration or definition? I’m just wondering if it’s getting compiled out of a development build somehow, as the linker error would suggest that the declaration exists, but the definition is missing.

There weren’t, but I had the function declared inline. I took that out just to see if that would make a difference and now it works. Do you know why that would be?