equivariant functions

[Robert Fraser]

Andrei Alexandrescu wrote:
> Jason House wrote:
>> Andrei Alexandrescu Wrote:
>>
>>> ore-sama wrote:
>>>> Andrei Alexandrescu Wrote:
>>>>
>>>>> typeof(s) stripl(const(char)[] s);
>>>>>
>>>>> This signature states that it returns the same type as an
>>>>> argument. I propose that that pattern means stripl can accept
>>>>> _any_ subtype of const(char)[] and return that exact type.
>>>>> Inside the function, however, the type of s is the type
>>>>> declared, thus restricting its use.
>>>> this conflicts with current definition of typeof. Currently 
>>>> typeof(s) stripl(const(char)[] s); should be interpreted exactly
>>>> as const(char)[] stripl(const(char)[] s); it's unclear that
>>>> typeof here gets type of actual argument rather than parameter.
>>>> Currently typeof applies to parameter.
>>> That is correct.
>>>
>>> Andrei
>>
>> I've never understood the reuse of keywords for new meanings. I much
>> prefer new keywords for new concepts.
> 
> Even in natural language identical words are reused for various 
> different meanings. This suggests that people would not feel comfortable 
> with a very large vocabulary. The size of vocabularies varies 
> dramatically, but if you look closer you'll see that languages with 
> large vocabularies tend to have simpler grammars, suggesting that a 
> language's overall complexity is a constant-sum game.
> 
> In programming languages growing the vocabulary indiscriminately is 
> worse because it chews into the vocabulary available to user-defined 
> symbols.
> 
> Also, whenever a feature is to be integrated into the language, it is 
> preferable if possible to integrate it under an existing concept instead 
> of "allocating" a new concept to it.
> 
> 
> Andrei

Just read this paper by Herb Sutter last night:

http://www.gotw.ca/publications/C++CLIRationale.pdf

In particular, the Bjarne Stroustrup quote is quite poignant:

""
My experience is that people are addicted to keywords for introducing 
concepts to the point where a concept  that doesn’t  have its own 
keyword is surprisingly  hard to  teach. This effect is more important 
and deep-rooted  than  people’s  vocally expressed  dislike for new 
keywords.  Given a choice and time to consider, people invariably choose 
the new keyword over a clever workaround.
       — B. Stroustrup (D&E, p. 119)
""

And Herb himself:

""
When a language feature is necessary, programmers strongly
prefer keywords. Normally, all C++ keywords  are also re-
served words, and taking a new one would break code that
is already using that word as an identifier (e.g., as a type or
variable name).

C++/CLI avoids adding reserved words so as to preserve the
goal of having pure extensions, but it also recognizes that
programmers expect keywords. C++/CLI balances  these re-
quirements by adding keywords where most are not reserved
words and so do not conflict with user identifiers.
""