#include <iostream>
#include <concepts>


template <typename T>
concept is_int = requires (T t) {
    sizeof(t) == sizeof(int);
};

is_int auto add(is_int auto a, is_int auto b) {
    return a + b;
}

int main() {
    int a = 5;
    int b = 10;
    std::cout << add(a, b);
}

Problems –

• identifier “concept” is undefined
• this declaration has no storage class or type specifier
• expected a ‘;’

Compiler – GCC 14.1.0 (with POSIX threads) + LLVM/Clang/LLD/LLDB 18.1.8 + MinGW-w64 12.0.0 (UCRT) – release 3
Platform – Windows

Visual Studio Code detects concepts as errors even though it compiles properly.