DRY緩存

Question

我期待幹出下面的C代碼：

if (i < SIZE_OF_V) { 
    if (V[i]) 
     K = V[d]; 
    else 
     K = V[d] = (expensive complicated call); 
} else { 
    K = (expensive complicated call); 
} 

有什麼建議？一個本地宏可以工作，但我更喜歡更現代的選擇。

Answer 1

你可以簡單地做

if (i < SIZE_OF_V && V[i]) { 
    K = V[d]; 
} else { 
    K = (expensive complicated call); 

    if (i < SIZE_OF_V) 
     V[d] = K; 
} 

你也可以把你的expensive complicated call在外部功能和CALLIT從兩個地方你if條件內：

int myExpensiveAndComplicatedCall() { 
    // Do things 
} 

if (i < SIZE_OF_V) { 
    if (V[i]) 
     K = V[d]; 
    else 
     K = V[d] = myExpensiveAndComplicatedCall(); 
} else { 
    K = myExpensiveAndComplicatedCall(); 
}