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Re: [RFC] A new mechanism to access the active field of unions

From: Bruno Haible
Subject: Re: [RFC] A new mechanism to access the active field of unions
Date: Sat, 06 Mar 2021 14:15:09 +0100
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>    a2) VAL isa IDENTIFIER
>    a3) VAL isa STR

a2 and a3 add new meanings to existing keywords. This route leads
to a hard-to-understand language, as C++ has shown. I would advise
against it.

> c) Like a Use a different keyword instead of `isa' in a2) and a3).
>    Maybe `holds'.
>    PRO: no potential confusion due to the overloading of `isa'.
>    CON: introduces a new keyword in the language.
> d) Use an attribute syntax instead of a binary operator syntax.
>    VAL'holds("foo")
>    PRO: no need to introduce new keyword.
>    PRO: can also be applied to structs (more orthogonal)
>    CON: in most cases the field name will be constant and it is
>          easier to just write an identifier.

I would vote for d. Testing for the existence of a property is not
such an important feature that would warrant an extra keyword.


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