Why abc printed?

help
1

Hello,
In the following code, why abc printed?

fn main() {
    let _a = if true { "abc" } else { "xy" };
    println!("{}", _a);
}

Thank you.

2

Are you having trouble understanding what if true means, or something about underscore-prefixed variables?

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3

What else would you expect to be printed?

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4

if … { … } else { … } is an expression (an IfExpression) that serves the same purpose as the ternary operator (… ? … : …) in many other languages.

See Ternary_conditional_operator#Conditional_assignment on Wikipedia.

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5

Hello,
Thank you so much for your reply.
This print abc, because if true is always true?

1 Like
6

Well, true is always true. And if condition { … } else { … } where the condition is true, will evaluate to the first block, and not the second.

I.e. it will execute the first block and return its result the whole IfExpression will evaluate to what the first block evaluates to.

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7

For further introduction to how if in Rust works, especially when used with let, see also:

Using if in a let Statement – if Expressions – Control Flow – The Rust Programming Language

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8

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