Curious. If you have "func();", is that an expression that is calling
the func function and discarding the result, or is that an ill-formed
forward-declaration of a function because it doesn't supply a trailing
return type? Similarly, how complex will it be for the parser to get
to "func()->" and still have it ambiguous as to whether this is the
beginning of a function declaration, or is this an expression that's
dereferencing the result of calling func()?

On Tue, Mar 18, 2025 at 6:56 PM Fady al Dhaim via Std-Proposals
<std-proposals_at_[hidden]> wrote:
>
> Hello,
>
> I’d like to propose a small but meaningful change to C++: making auto optional in trailing return types.
>
> 1. Motivation
>
> Currently, auto is required in functions that use trailing return types:
>
> auto func() -> int; // Required
>
> However, this requirement is redundant and misleading because:
>
> The return type is explicitly specified (int), so auto adds no value.
> auto implies type deduction, but no deduction is happening here.
>
> A more natural syntax would allow:
>
> func() -> int; // More intuitive Right?
>
> Not only does this improve readability and consistency with standard function declarations, but it also aligns well with Software Engineering Structural Diagrams, such as UML Class Diagrams and Object Diagrams.
>
> In UML Class Diagrams, method return types are typically represented after the function name, similar to how trailing return types work in C++. Allowing func() -> int; without auto makes the C++ syntax closer to UML representations, enhancing clarity and traceability between a codebase and its corresponding UML models.
>
> ________________________________
>
> 2. Why This Won’t Break Existing Code
>
> This proposal is backward-compatible because:
>
> auto is already optional in normal return types:
>
> int func();
>
> This change is purely syntactic—it does not affect semantics.
>
> Existing code using auto remains fully valid.
> auto func() -> int; // Remains valid
> auto func() -> decltype(some_expression); // Also valid
>
> Thus, this proposal only removes an unnecessary restriction without introducing breaking changes.
>
> ________________________________
>
> 3. Proposed Change
>
> Modify the C++ grammar so that functions using trailing return types no longer require auto.
> This would allow:
>
> Current (C++ Standard Today)
>
> auto func() -> int; // Required
>
> Proposed (New Syntax Allowance)
>
> func() -> int; // Allowed
>
> This makes the syntax more consistent with regular function declarations.
>
> ________________________________
>
> 4. Next Steps
>
> Would this be a reasonable proposal for a future C++ standard update?
> I’d love to hear your thoughts and suggestions on how this could be refined further.
>
> Best regards,
> Fady al Dhaim
>
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