F# = what?

I was reading through my most recent book addiction purchase (Programming F#) and I came across something I thought was interesting.

The (=) operator, basically in any other language assigns something to another thing, but in F# it’s actually a comparison operator. In C# (==) is used for comparison and (=) is used for assignment. If you forget the second (=), you can create a fun bug, for example:

bool canDoSomething = false;
if (canDoSomething = true)
{
DoSomething();
}


In this example the if statement is assigning true to the canDoSomething variable, which evaluates to true if the assignment is successful.

The if statement should really be:

if (canDoSomething == true)


In F# you “assign” using the let statement:

let canDoSomething = true


Moral of the story is, if you program in F#, it’s easier to avoid this bug. However, watch your step when going from F# to another language.

For a little bit more information, check out this list of F# arithmetic operators:
http://msdn.microsoft.com/en-us/library/dd469493%28VS.100%29.aspx