2.9. Modifiers#

Syntax#

ModifierDefinition = (* modifier_keyword: *) MODIFIER_KEYWORD
                     (* name: *) IDENTIFIER
                     (* parameters: *) ParametersDeclaration?
                     (* attributes: *) ModifierAttributes
                     (* body: *) FunctionBody;

ModifierAttributes = (* item: *) ModifierAttribute*;

ModifierAttribute = (* variant: *) OverrideSpecifier (* Introduced in 0.6.0 *)
                  | (* variant: *) VIRTUAL_KEYWORD; (* Introduced in 0.6.0 *)

ModifierInvocation = (* name: *) IdentifierPath
                     (* arguments: *) ArgumentsDeclaration?;

Function Modifiers#

Function modifiers can be used to amend the semantics of functions in a declarative way:

contract MyContract {
    modifier onlySeller() {
        require(msg.sender == seller, "Only seller can call this.");
        _; // Function body will be inserted here
    }

    function myFunction() public view onlySeller {
        // Code here will be executed after `onlySeller` is executed.
    }
}

Unlike functions, modifiers cannot be overloaded.