auto res = if (1) {
   // some code

   return 1;
} else {
   // some code

   return 0;
}


auto res = switch ( idx) {
   case 0: { /* some code */; return 33; }
   case 1: { /* some code */; return 44; }
   default: return -1;
}

auto res = []( auto idx ) { switch( idx ) {
    case 0: { /* some code */; return 33; }
    case 1: { /* some code */; return 44; }
    }}( idx );

#define EXPRESS(...) BEGIN_EXPRESS __VA_ARGS__ END_EXPRESS
// на тот случай, если препроцессор на скобках внутри аргументов с ума сойдёт,
#define BEGIN_EXPRESS  ([&](){
#define END_EXPRESS    }())

int main() {
  cout << EXPRESS( cout << "hello"; if (1 > 2) return 123; cout << "world"; return 456; ) << endl;
  cout << BEGIN_EXPRESS
    cout << "hello";
    if (1 > 2) return 123;
    cout << "world";
    return 456;
  END_EXPRESS << endl;
}

К>#define EXPRESS(...) BEGIN_EXPRESS __VA_ARGS__ END_EXPRESS
К>

int x = ${ if(1) return 42; else return 0; };

struct Aux
{
    template<typename F>
    auto operator*(F &&f)
    {
        return f();
    }
};

#define $ Aux{} * [&]

X>auto res = if (1) {
X>   // some code

X>   return 1;
X>} else {
X>   // some code

X>   return 0;
X>}


X>auto res = switch ( idx) {
X>   case 0: { /* some code */; return 33; }
X>   case 1: { /* some code */; return 44; }
X>   default: return -1;
X>}
X>

    let boo = false;
    let foo = if boo {
        1
    } else {
        2
    };
    
    let foo2 = match foo {
        1 => 2,
        2 => 3,
        _ => -1,
    };
    
    let foo3 = {
        let a = 1;
        a + 3
    };

auto res = if (1) {
   // some code
   1;
} else {
   // some code
   0;
}