Help refactoring this C# function

Question

I have written functions that look like this:

bool IsDry(bool isRaining, bool isWithUmbrella) {     if (isRaining) {         if (isWithUmbrella)             return true;         else             return false;     }     else         return true; } 

I need to check, if it's raining, then the person needs to carry an umbrella in order to keep dry (don't laugh, this is just an example, our actual business rules are more serious than this).

How can I refactor this, because right now it looks clumsy.

Thanks for the help, guys! =)

Answer 1

It looks like the business rule you're trying to enforce is:

P IMPLIES Q 

This is logically equivalent to:

(NOT P) OR Q 

Thus, you can simply write:

bool IsDry(bool isRaining, bool isWithUmbrella) {     return !isRaining || isWithUmbrella; } 

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On (not) thinking negatively

Depending on the predicate, it may also be simpler to first think in terms of its negation.

NOT (P IMPLIES Q) 

We now substitute the identity above:

NOT ((NOT P) OR Q) 

Now we can apply DeMorgan's Law:

P AND (NOT Q) 

Since this is the negation, we must negate this to get back to the positive. The double negation may seem confusing at first, but going back to the example, we have:

bool IsDry(bool isRaining, bool isWithUmbrella) {     bool isWet = (isRaining && !isWithUmbrella);     return !isWet; } 

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Additional tips

Here are some examples of common boolean expression rewriting:

BEFORE                                  | AFTER ________________________________________|________________________________________                                         | if (condition == true) ...              | if (condition) ... ________________________________________|________________________________________                                         | if (condition == false) ...             | if (!condition) ... ________________________________________|________________________________________                                         | if (condition) {                        | return condition;     return true;                        | } else {                                |     return false;                       | }                                       | ________________________________________|________________________________________                                         | if (condition1) {                       | return (condition1 && condition2    if (condition2) {                    |             && condition3);       if (condition3) {                 |          return true;                   |       } else {                          |          return false;                  |       }                                 |    } else {                             |       return false;                     |    }                                    | } else {                                |    return false;                        | }                                       | ________________________________________|________________________________________                                         | return (condition1 && !condition2) ||   | return condition1 != condition2;    (condition2 && !condition1);         | // or  condition1 ^ condition2; 

Note that the predefined ^ in C# is the exclusive-or operator, even for integral types (i.e. it's not an exponentiation operator). The predefined && and || are conditional logical operators that performs "short-circuit" evaluation.

See also

• C# ‘or’ operator?
• What is the diffference between the | and || or operators?
• What is the best practice concerning C# short-circuit evaluation?
• Short circuiting statement evaluation — is this guaranteed? [C#]
• When to use ^ operator