[porting] IAR's overload resolution struggles with `etl::span::span(etl::array&)`

[dhebbeker]

I try to construct a etl::span from an etl::array. This shouldn't be any issue as an appropriate constructor exists.

I have an example on Compiler Explorer which compiles successfully. It uses

• avr gcc 13.2.0
• ETLCPP 20.38.0
• C++98

In short it does

etl::array<int,10> mArray;
etl::span<int> mSpan(mArray);

Now with the compiler I have to use I get this error:

Error[Pe309]: more than one instance of constructor "etl::span<T, 65535U>::span [with T=int]" matches the argument list:
            function template "etl::span<T, 65535U>::span(etl::array<U, N> &, etl::enable_if<etl::is_same<int, etl::remove_cv<U>::type>::value, void>::type *) [with T=int]" 
            function template "etl::span<T, 65535U>::span(TContainer &, etl::enable_if<<expression>, void>::type *) [with T=int]" 
            argument types are: (Array) 

• IAR C/C++ Compiler for AVR 6.70.1 (6.70.1.929)
• ETLCPP 20.38.1 (7fdaa7c9a461bfd191ee34ad950e01c919c8e7cd)
• Extended Embedded C++ (a dialect of C++98)

The problem seems to be that IAR's overload resolution recognizes both constructor candidates as equally good during overload resolution.

Before suggesting a patch I wonder: Why are there both definitions:

• span(etl::array<U, N>& a) in line 534 and
• span(TContainer& a) in line 592

The latter does cover the first case equally well?

I think the code is currently correct as it is. But it contains (unnecessary?) overloads which the IAR chokes on.

[jwellbelove]

I have a fix that I will push very soon.

[dhebbeker]

Thank you!

[jwellbelove]

Actually, I may have been too hasty. I've been working on #754, not this one. What was your suggested fix?

[jwellbelove]

You are correct, span(TContainer& a) works fine for std & etl arrays.

[dhebbeker]

I would have removed span(etl::array<U, N>& a). But I see you did this already in 01d96609cf5193f9a5b8f90cd8a1a23a5ea05631 👍

I tested that commit with the IAR compiler mentioned above. The code (same as the one referenced in the description) now compiles without compiler errors 🥳

🙏 Thank you!

[jwellbelove]

Fixed 20.38.2