Is func_does_not_depend_on_T code-generated once per every T used ? If so, does it make sense to (for compile time), move func_does_not_depend_on_T to a non-generic environment? (Or is this borderline stupid micro optimization) ?
As far as I know, it's actually worse than that... Say you use a Foo<u32> in your code, the compiler won't just generate a single instantiation of func_does_not_depend_on_T, it'll generate a new copy of Foo::<u32>:: func_does_not_depend_on_T for every codegen unit that happens to use a Foo<u32>.
When you consider that the compiler breaks your crate up into multiple codegen units so machine code can be generated and optimised in parallel, that means you might compile Foo<u32> several times.
That's one of the reasons the standard library uses the inner function pattern all over the place: