Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Thiago Adams <thiago.adams@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: constexpr keyword is unnecessary
Date: Sat, 19 Oct 2024 22:56:03 -0300
Organization: A noiseless patient Spider
Lines: 35
Message-ID: <vf1nvj$83oo$1@dont-email.me>
References: <veb5fi$3ll7j$1@dont-email.me>
 <877ca5q84u.fsf@nosuchdomain.example.com> <vf0ijd$3u54q$1@dont-email.me>
 <vf0l98$3un4n$1@dont-email.me> <vf1216$p0c$1@dont-email.me>
 <87y12jpxvl.fsf@nosuchdomain.example.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Injection-Date: Sun, 20 Oct 2024 03:56:04 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="26ddf3a2db6c9a64a775b4526ef6ea85";
	logging-data="266008"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+RqFvrYZzan3UzWYBv2ppm6DGF1fFSH/4="
User-Agent: Mozilla Thunderbird
Cancel-Lock: sha1:8SGgQlVwDVPrfdnxBOOFDtgQ9ws=
Content-Language: en-GB
In-Reply-To: <87y12jpxvl.fsf@nosuchdomain.example.com>
Bytes: 2398

>Em 10/19/2024 6:48 PM, Keith Thompson escreveu:
> Thiago Adams <thiago.adams@gmail.com> writes:
> Let's pretend that when "const" was introduced in C89, it was spelled
> "readonly", which more closely reflects its meaning.  Would you suggest
> that
> 
>      readonly int n = 42;
> 
> should make n a constant expression?
> 

I used to find const confusing, as it sometimes meant 'read-only' and 
other times 'immutable.'
Now, it seems less confusing to me. When const is used with variables 
that can be initialized (init-declarator), it acts as 'immutable,' 
meaning the storage is constant.
In other contexts, like function parameters, const means 'read-only' 
because we don’t know if the storage is constant or not.

It’s also interesting to note that constexpr acts as a storage 
qualifier. What the compiler needs to know when evaluating an expression 
at compile time, without depending on flow analysis, is the guarantee 
that the object is immutable. This makes it safe to use the value it has 
at initialization when the initialization is also a compile time expression.

const used in variables that can be initialized gives the compiler the 
same guarantees.