Block expressions - The Rust Reference

# Block expressions

> Syntax
> BlockExpression :
> `{`
> InnerAttribute*
> Statement*
> Expression?
> `}`

A block expression is similar to a module in terms of the declarations that are possible, but can also contain statements and end with an expression. Each block conceptually introduces a new namespace scope. Use items can bring new names into scopes and declared items are in scope for only the block itself.

A block will execute each statement sequentially, and then execute the expression, if given. If the block doesn't end in an expression, its value is `()`:

    # #![allow(unused_variables)]
    #fn main() {
    let x: () = { println!("Hello."); };
    #}

If it ends in an expression, its value and type are that of the expression:

    # #![allow(unused_variables)]
    #fn main() {
    let x: i32 = { println!("Hello."); 5 };

    assert_eq!(5, x);
    #}

Blocks are always value expressions and evaluate the last expression in value expression context. This can be used to force moving a value if really needed.

## `unsafe` blocks

> Syntax
> UnsafeBlockExpression :
> `unsafe` BlockExpression

See `unsafe` block for more information on when to use `unsafe`

A block of code can be prefixed with the `unsafe` keyword, to permit calling `unsafe` functions or dereferencing raw pointers within a safe function. Examples:

    # #![allow(unused_variables)]
    #fn main() {
    unsafe {
        let b = [13u8, 17u8];
        let a = &b[0] as *const u8;
        assert_eq!(*a, 13);
        assert_eq!(*a.offset(1), 17);
    }

    # unsafe fn f() -> i32 { 10 }
    let a = unsafe { f() };
    #}