Parameterized methods can shadow other method without error/warning

[mauro3]

Parameterized methods are more specific than non-parameterized ones:

julia> g(x) = 1
g (generic function with 1 method)

julia> g{X}(x::X) = 2
g (generic function with 2 methods)

julia> g(4)
2

I don't think there is any way to call the first method of g.

Similarly for several arguments:

julia> h(x,y) = 1
h (generic function with 1 method)

julia> h{X}(x::X,y) = 2
h (generic function with 2 methods)

julia> h{X,Y}(x::X,y::Y) = 3
h (generic function with 3 methods)

julia> h{Y}(x,y::Y) = 4
h (generic function with 4 methods)

julia> h(4,5)
2

One solution is to consider above methods ambiguous and throw MethodError ... is ambiguous. on call. Another solution is to make those method definitions overwrite the previous one. Probably should be in sync with #8974.

X-ref: https://groups.google.com/d/msg/julia-users/-ldkZlbg76Q/pYRNT4eIBAAJ

[JeffBezanson]

Yes, #8974 will provide a definitive type equality test that will allow these method overwrites to happen.

[JeffBezanson]

closed by #18457

[vtjnash]

This is still an issue, since type-equal is not the same as sig-equal due to the extra parameters-must-match rule. That can cause us to incorrectly delete a method that may still be needed, or replace a method with one that is not equivalent (mostly resulting from Varargs).

[JeffBezanson]

Closing in favor of #21026, which is more specifically about that.