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Re: [std-proposals] A draft for modern switch

From: Filip <fph2137_at_[hidden]>
Date: Wed, 21 May 2025 09:34:24 +0200
I agree, it seems like a better idea to have switch in non constexpr context available, to act like a nicer option acting like if else.

Maybe I’m missing the key functionality of match, but it looks like a different syntax for something that we already have.

I agree that assignment with match looks like a good idea, why wouldn’t we add that to the switch statement?

string b = “hello”;
auto var = switch(b){
                    case “hi”: { return 42; }
                    case “hello”: { return 43; }
                     default: { return 0; } // probably should be mandatory
                  };

Cheers, Filip

Wiadomość napisana przez Zhao YunShan via Std-Proposals <std-proposals_at_[hidden]> w dniu 21 maj 2025, o godz. 04:15:




switch is a concept familiar to all programmers. Most languages use switch with strings, including JS, Golang, PHP, etc.
match seems a bit unusual in comparison.


Indeed, using a constexpr hash function can construct a perfect hash, but my idea is to have the compiler handle this task rather than doing it manually myself.



Regards


At 2025-05-21 01:42:45, "Nikolay Mihaylov" <nmmm_at_[hidden]> wrote:

my 5 cents

The idea of switch is not to make the life of the programmer easier, the idea is to make a jump table so this can be compiled in 2-3 instructions.

There is a new control flow statement called "match". lots of languages uses it already:

btw, you can use switch with strings, kind of, using constexpr hash function and assuming not hash collisions (manual perfect hash)

Regards

Nikolay

On Tue, May 20, 2025 at 8:29 PM Zhihao Yuan via Std-Proposals <std-proposals_at_[hidden]> wrote:

--
Zhihao Yuan, ID lichray
The best way to predict the future is to invent it.
_______________________________________________

On Tuesday, May 20th, 2025 at 4:38 AM, Zhao YunShan via Std-Proposals <std-proposals_at_[hidden]> wrote:

    In C++, the switch statement is a fundamental control-flow construct originally designed to work only with integer types (int, char, enum, etc.). However, in real-world development, programmers often need to handle string-based (std::string) branching logic. While the standard syntax does not natively support strings, well-structured design patterns can still leverage switch-like behavior to replace lengthy if...else if chains, significantly improving code readability and conciseness.

#include <iostream>
#include <string>
int main()
{
    std::string router;
    switch (router)
    {
    case "cpp":
        std::cout << "cpp router selected.";
        break;
    case "hpp":
        std::cout << "hpp router selected.";
        break;
    default:
        std::cout << "Unknown router type.";
        break;
    }
    return 0;
}


By leveraging compile-time static analysis, switch statements can be optimized into various efficient data structures:

    Jump tables for few cases,
    Balanced binary search for many branches,
    Hash tables where supported.

This ensures optimal time complexity (O(1) to O(log n)) even with large branch sets.


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Received on 2025-05-21 07:34:42