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|
{
"rendered": "error[E0277]: can't compare `{integer}` with `&str`\n --> src/main.rs:2:5\n |\n2 | assert_eq!(1, \"love\");\n | ^^^^^^^^^^^^^^^^^^^^^^ no implementation for `{integer} == &str`\n |\n = help: the trait `std::cmp::PartialEq<&str>` is not implemented for `{integer}`\n = note: this error originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)\n\n",
"children": [
{
"children": [],
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"level": "help",
"message": "the trait `std::cmp::PartialEq<&str>` is not implemented for `{integer}`",
"rendered": null,
"spans": []
}
],
"code": {
"code": "E0277",
"explanation": "\nYou tried to use a type which doesn't implement some trait in a place which\nexpected that trait. Erroneous code example:\n\n```compile_fail,E0277\n// here we declare the Foo trait with a bar method\ntrait Foo {\n fn bar(&self);\n}\n\n// we now declare a function which takes an object implementing the Foo trait\nfn some_func<T: Foo>(foo: T) {\n foo.bar();\n}\n\nfn main() {\n // we now call the method with the i32 type, which doesn't implement\n // the Foo trait\n some_func(5i32); // error: the trait bound `i32 : Foo` is not satisfied\n}\n```\n\nIn order to fix this error, verify that the type you're using does implement\nthe trait. Example:\n\n```\ntrait Foo {\n fn bar(&self);\n}\n\nfn some_func<T: Foo>(foo: T) {\n foo.bar(); // we can now use this method since i32 implements the\n // Foo trait\n}\n\n// we implement the trait on the i32 type\nimpl Foo for i32 {\n fn bar(&self) {}\n}\n\nfn main() {\n some_func(5i32); // ok!\n}\n```\n\nOr in a generic context, an erroneous code example would look like:\n\n```compile_fail,E0277\nfn some_func<T>(foo: T) {\n println!(\"{:?}\", foo); // error: the trait `core::fmt::Debug` is not\n // implemented for the type `T`\n}\n\nfn main() {\n // We now call the method with the i32 type,\n // which *does* implement the Debug trait.\n some_func(5i32);\n}\n```\n\nNote that the error here is in the definition of the generic function: Although\nwe only call it with a parameter that does implement `Debug`, the compiler\nstill rejects the function: It must work with all possible input types. In\norder to make this example compile, we need to restrict the generic type we're\naccepting:\n\n```\nuse std::fmt;\n\n// Restrict the input type to types that implement Debug.\nfn some_func<T: fmt::Debug>(foo: T) {\n println!(\"{:?}\", foo);\n}\n\nfn main() {\n // Calling the method is still fine, as i32 implements Debug.\n some_func(5i32);\n\n // This would fail to compile now:\n // struct WithoutDebug;\n // some_func(WithoutDebug);\n}\n```\n\nRust only looks at the signature of the called function, as such it must\nalready specify all requirements that will be used for every type parameter.\n"
},
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"text": " panic !"
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"text": " (r#\"assertion failed: `(left == right)`"
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"text": " right: `{:?}`\"#,"
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"text": " }) ; ($ left : expr, $ right : expr,) =>"
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"text": " panic !"
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"text": " & * left_val, & * right_val, $ crate :: format_args !"
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"text": " assert_eq!(1, \"love\");"
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}
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}
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