Assignment operator in f#

问题:

i have seen in ruby as well powershell programming we can assign variables like a,b=b,a . it actually swaps the variable .

Is this possible in f# if so please guide me with some reference

回答1:

Generally, F# doesn't allow variable re-assignment. Rather it favors immutable named values via let bindings. So, the following is not possible:

let a = 3
a = 4

Unless you explicitly mark a as mutable:

let mutable a = 3
a <- 4

However, F# does allow in most situations variable "shadowing". The only restriction to this is that it can not be done on top level modules. But, within a function, for example, the following works fine:

let f () =
    let a,b = 1,2
    let a,b = b,a //"swap"
    a,b