Kotlin has more constructs that are expressions th...

# announcements

[streetsofboston]

Kotlin has more constructs that are expressions than Java has (e.g. if, when, try expressions in Kotlin, but not in Java).

What was the reason that the assignment operator = is not an expression?

[ilya.gorbunov]

Mainly because = is used in named arguments syntax:
foo(arg = value)
This is a call of foo with arg argument, rather than a call of foo with the result of assignment of value to some arg variable/property.

[streetsofboston]

Ah! Thank you!
I thought it was done to discourage coding expressions with side-effects. But then I realized that (value++) would exactly be such an expression 🙂

[ghedeon]

It also prevents accidental mistakes when == is intendet, right?

[karelpeeters]

@ghedeon How often does that happen? It would only compile for a boolean and you never do == true anyway. You can compare two booleans but that's even more rare.

[ilya.gorbunov]

Note that you can achieve the same effect as assignment expression with also function:
foo(value.also { someVar = it })