Error map
E0271: type mismatch resolving associated type Rust: error[E0271]: type mismatch resolving `<impl Iterator as Iterator>::Item == i32`
Rust · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
C++: error: invalid conversion from 'const char*' to 'char*' [-fpermissive]
C++ forbids silently dropping `const` or converting between unrelated pointer types — typically a string literal assigned to `cha…
C++: error: call of overloaded 'f(int)' is ambiguous
Two or more overloads fit equally well, so the compiler refuses to guess which function you meant.
C++: error: 'string' does not name a type
Where the compiler expected a type, it found a name it does not know as one — a missing header, namespace, or class declared late…
C/C++: warning: comparison of integer expressions of different signedness: 'int' and 'size_t' [-Wsign-compare]
A signed integer is compared with an unsigned one; the signed value is converted to unsigned, so a negative number becomes huge.
Rust: error[E0308]: mismatched types — expected `X`, found `Y`
A value’s type doesn’t match what the context expects — common with &str vs String, Option/Result vs plain values, and integer ty…
C++: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
You compared a string literal or pointer with a character or integer — typically `ch == "y"` instead of `ch == 'y'`.
C++: error: narrowing conversion of 'x' from 'int' to 'char' inside { } [-Wnarrowing]
Brace initialisation `{}` refuses conversions that can lose data, such as `double` to `int` or a runtime `int` to `char`.
C++: error: template argument deduction/substitution failed / couldn't deduce template parameter
The compiler could not work out the template arguments from your call — the arguments disagree, the type can't be deduced, or a c…
Rust: error[E0277]: the trait bound `Foo: Display` is not satisfied / `Rc<RefCell<T>>` cannot be sent between threads safely
A type doesn't implement a trait required by a function, macro or generic bound.
Cargo: Blocking waiting for file lock on package cache / on build directory
Another cargo process (or rust-analyzer/IDE) holds the lock, so this command waits.
Go: invalid operation: a + b (mismatched types int and float64)
You combined two values of different types; Go never converts numeric types implicitly.
Go: cannot use "5" (untyped string constant) as int value in argument to f
A value's type is not assignable to the type required by the variable, parameter or return value.
Two steps away (30)
C++: error: no matching function for call to 'f(int, const char*)'
No overload of the function accepts the arguments you passed — wrong count, wrong types, or a missing conversion.
C++: error: passing 'const X' as 'this' argument discards qualifiers [-fpermissive]
A const object (or const reference) is calling a method that is not declared const, which could modify it.
Rust: error[E0412]: cannot find type `User` in this scope
A type name isn't defined or imported in the current module.
C++: error: no match for 'operator<<' (operand types are 'std::ostream' and 'X')
You used an operator on a type that does not define it — most often printing your own class with `
C++: error: use of deleted function 'X::X(const X&)' — copying a non-copyable type
The code needs a function (usually a copy constructor or assignment) that was deleted explicitly or implicitly, as for `std::uniq…
C++: error: 'int X::secret' is private within this context
Code outside the class tried to use a private (or protected) member.
Go: declared and not used: x / "fmt" imported and not used
Go refuses to compile code with unused local variables or unused imports.
C/C++: error: expected ';' before 'x' — missing semicolon
The compiler reached a token where a statement should have ended — almost always a missing semicolon on the line above.
C++: error: 'x' was not declared in this scope (undeclared identifier)
The compiler met a name it has never seen: it is misspelled, declared later, out of scope, or its header or namespace is missing.
C/C++: warning: control reaches end of non-void function [-Wreturn-type]
A function that promises a return value can finish without returning one on some path — undefined behaviour in C++.
C: warning: format '%d' expects argument of type 'int', but argument 2 has type 'long int' [-Wformat=]
The `printf`/`scanf` format specifier does not match the argument's type, which is undefined behaviour and prints garbage or cras…
C: warning: implicit declaration of function 'foo' [-Wimplicit-function-declaration]
In C you called a function the compiler has not seen declared — usually a missing `#include`. Newer compilers treat it as an erro…
AttributeError: 'X' object has no attribute 'y'
You accessed an attribute or method that doesn’t exist on that object type.
java.lang.ClassCastException: class A cannot be cast to class B
An object was cast to a type it isn’t.
TS7016: Could not find a declaration file for module 'x'. 'x.js' implicitly has an 'any' type.
The JavaScript package has no TypeScript types bundled and no @types package installed.
Rust: error[E0369]: binary operation `+` cannot be applied to type `Foo` / cannot add `&str` to `&str`
An operator (`+`, `==`, `
C/C++: runtime error: signed integer overflow / null pointer / shift exponent too large (UndefinedBehaviorSanitizer)
UBSan detected code that triggers undefined behaviour (overflow, null dereference, out-of-bounds index, bad shift, misaligned acc…
C++: error: need 'typename' before 'T::iterator' because 'T' is a dependent scope
Inside a template, a name like `T::iterator` could be a type or a value, so C++ requires the `typename` keyword to say it is a ty…
Rust: error[E0599]: no method named `push_str` found for struct `Vec<String>` in the current scope
The type doesn't have that method — wrong type, trait not in scope, or missing derive/feature.
Rust: error[E0004]: non-exhaustive patterns: `None` not covered
A `match` doesn't handle every possible value of the type.
Rust: error[E0061]: this function takes 2 arguments but 1 argument was supplied
A call has too few or too many arguments for the function signature.
Rust: error[E0499]: cannot borrow `v` as mutable more than once at a time
Two mutable references to the same value were alive at once, which Rust forbids.
Rust: error[E0505]: cannot move out of `s` because it is borrowed
You moved a value while a reference to it was still in use.
Rust: error[E0507]: cannot move out of `self.name` which is behind a shared reference
You tried to take ownership of a value through a reference (or from a Vec/Option behind `&`).
Go: ./main.go:5:2: "os" imported and not used
The file imports a package that no code in that file uses; Go treats this as a compile error, not a warning.
Go: cannot assign to struct field users["bob"].Age in map
Map values are not addressable, so you cannot modify a field of a struct stored directly in a map.
Go: cannot use &Dog{} (value of type *Dog) as Animal value: *Dog does not implement Animal (missing method Speak)
A type was used as an interface but lacks a method or has it with a different signature or receiver type.
Go: ./main.go:12:2: undefined: handler
The compiler cannot find an identifier — a typo, a missing import, or it lives in another file/package that wasn't built.
Go: ./main.go:18:1: missing return
A function with a return type can reach its end without a return statement on some path.
Go: ./main.go:9:6: no new variables on left side of :=
`:=` declares variables, but all names on the left already exist in the same scope.
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