You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lib.rs
    path of file: ./repos/ink/integration-tests/lang-err-integration-tests/call-builder-delegate
    
    the code of the file until where you have to start completion: //! # Integration Tests for `LangError`
//!
//! This contract is used to ensur
    
        pub fn invoke(&mut self, code_hash: Hash, selector: [u8; 4]) -> i32 {
            use ink::env::call::build_call;

            build_call::<DefaultEnvironment>()
                .delegate(code_hash)
                .exec_input(ExecutionInput::new(Selector::new(selector)))
                .returns::<i32>()
                .invoke()
        }