Keyword true 

A value of type bool representing logical true.

Logically true is not equal to false.

Control structures that check for true

Several of Rust’s control structures will check for a bool condition evaluating to true.

• The condition in an if expression must be of type bool. Whenever that condition evaluates to true, the if expression takes on the value of the first block. If however, the condition evaluates to false, the expression takes on value of the else block if there is one.

• while is another control flow construct expecting a bool-typed condition. As long as the condition evaluates to true, the while loop will continually evaluate its associated block.

• match arms can have guard clauses on them.