Perhaps this is intended by design, but this proposal syntactically disallows the ability to have a run-time variable expression, or even a named compile-time constant (e.g. #define symbol, or const int x = 2;) as the index of the tuple element reference.

Using syntax like my_tuple[0] or similar, even if most or all implementations would likely limit the expression to a compile-time known value that is int (also bit<W> or int<W>), would enable code like:

#define MY_FAVORITE_INDEX 2
const int second_favorite_index = 5;

     a = my_tuple[MY_FAVORITE_INDEX];
     b = my_tuple[second_favorite_index];

Yes, this is by design, with a dynamic index we cannot statically tell the field type.

So compile-time known value is needed, understood. But an expression still might be useful for developers? We allow compile-time known value expressions in bit slices today, and in place of the W in bit<W> types.

This syntax won't work for expressions.

Fixes #864

I approve but let's discuss at the July LDWG.

+1 for array indexing syntax, even if the indices are restricted to compile-time constant expressions.

Actually, upon reflection, I think array indexing is much better than f0, f1, etc.

Would it make sense to introduce optional field names that can be defined by the programmer, while using f0, f1, etc. as a backup?

@vgurevich can you elaborate on your proposal?

@mbudiu-vmw -- something like:

result = Hash.get({src_ip = hdr.ipv4.src_addr, dst_ip=hdr.ipv4.dst_addr, protocol=hdr.ipv4.proto});

This is an anonymous struct, not a tuple. We have an issue filed for supporting anonymous structs, and you are listed as an owner.

The spec should say whether tuple fields can be left values.

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@jnfoster : made the requested typo fix. If you approve we can merge this.