{"id":1191,"hash":"690e56b6bbd76cbcc83819e9326f837ac6842d0f8c91fa6a992ce2755c471107","pattern":"Error: The trait `Handler&lt;_&gt;` is not implemented for `fn() -&gt; HttpResponse","full_message":"If I was to use this code on Actix Web 3 it would work, but I need to use the latest stable release... so 4^.\n\nHere is the snippet in question (actually this is the entirety of my code):\n\nuse actix_web::{web, App, HttpResponse, HttpServer, ResponseError, Handler};\n\n fn hello_world() -> HttpResponse {\n    HttpResponse::Ok().body(\"Hello, Mr. World\") }\n \n #[actix_web::main] async fn main() -> std::io::Result<()> {\n     HttpServer::new(move || App::new().route(\"hello\", web::get().to(hello_world)))\n         .bind(\"0.0.0.0:8000\")?\n         .run()\n         .await\n }\n\nHere is the error I get in version 4 or higher.\n\nweb::get().to(hello_world)))\n    |                                                                  -- ^^^^^^^^^^^ the trait `Handler<_>` is not implemented for `fn() -> HttpResponse {hello_world}`\n    |                                                                  |\n    |                                                                  required by a bound introduced by this call\n    |\nnote: required by a bound in `Route::to`\n   --> /Users/xavierfontvillasenor/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-web-4.1.0/src/route.rs:211:12\n    |\n211 |         F: Handler<Args>,\n    |            ^^^^^^^^^^^^^ required by this bound in `Route::to`\n\nWhen I add the trait,\n\nimpl Handler<T> for HttpResponse {\n    type Output = ();\n    type Future = ();\n\n    fn call(&self, args: T) -> Self::Future {\n        todo!()\n    }\n}\n\nI get\n\nimpl Handler<T> for HttpResponse {\n  |     -        ^ not found in this scope\n  |     |\n  |     help: you might be missing a type parameter: `<T>`\n\nThis works in V.3 why not now? What can I do?","ecosystem":"cargo","package_name":"actix-web","package_version":null,"solution":"You are not meant to implement Handler yourself, the issue is that handlers are required to be async functions, see the docs for more details:\n\n// 👇\nasync fn hello_world() -> HttpResponse {\n    HttpResponse::Ok().body(\"Hello, Mr. World\")\n}","confidence":0.95,"source":"stackoverflow","source_url":"https://stackoverflow.com/questions/72748775/error-the-trait-handler-is-not-implemented-for-fn-httpresponse","votes":10,"created_at":"2026-04-19T04:52:34.053217+00:00","updated_at":"2026-04-19T04:52:34.053217+00:00"}