"if (a() && b != null)" will "a()" always be evaluated?

Question

I have such code:

if (a() && b != null) {     b.doSomething(); } 

I need side effect of a() even if b is null. Is it guaranteed by C#? Or C# may omit a() call if b is null?

Answer 1

Yes, a() will always be evaluated.

Since the condition is evaluated from left to right, a() will always be evaluated, but b != null will only be evaluated if a() returns true.

Here's an exact specification reference for you, from the C# Language Specification version 3.0. My emphases and elisions.

7.11.1 Boolean conditional logical operators

When the operands of && or || are of type bool [...] the operation is processed as follows:

• The operation x && y is evaluated as x ? y : false. In other words, x is first evaluated and converted to type bool. Then, if x is true, y is evaluated and converted to type bool, and this becomes the result of the operation. Otherwise, the result of the operation is false.

Answer 2

Yes, expressions are evaluated from left to right; so a() will always be called.

See the C# language spec (ECMA 334, paragraph 8.5):

Except for the assignment operators, all binary operators are left-associative, meaning that operations are performed from left to right. For example, x + y + z is evaluated as (x + y) + z.