Block expressions - The Rust Reference

# Block expressions

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 rvalues and evaluate the last expression in rvalue context. This can be used to force moving a value if really needed.

## `unsafe` blocks

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.