Bug 17242 – Specialized templates defined inside functions fail lookup, moving them outside makes them work

This code causes a compilation error: void main () { template Floating1(T) if (is(T == cfloat) || is(T == cdouble) || is(T == creal)) { } template Floating1(T) if (is(T == float) || is(T == double) || is(T == real)) { } } Error: declaration Floating1(T) if (is(T == float) || is(T == double) || is(T == real)) is already defined Obviously moving the two templates to top level works. This is a violation of the "turtles all the way down" principle.

It also is the case with nested functions: int foo(int i) { int bar(int a) { return a; } int bar(uint b) { return b; } return bar(i); } Name lookup is different inside functions. Overloading function definitions is not allowed, neither are forward references: int foo(int i) { return bar(i); int bar(int a) { return a; } }

Indeed, according to the spec [1] this is invalid. [1] https://dlang.org/spec/function.html#nested-declaration-order