Error map
Cannot convert value of type Swift: Cannot convert value of type 'X' to expected argument type 'Y'
iOS · layer 1, On your device
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Directly related (12)
Deprecated: Implicit conversion from float 2.5 to int loses precision
PHP 8.1+ warns when a float with a fractional part is silently converted to int (array keys, % operator, int parameters).
System.InvalidCastException: Unable to cast object of type 'X' to type 'Y'
An explicit cast failed because the object’s runtime type isn’t the target type.
Fatal error: Uncaught TypeError: foo(): Argument #1 ($x) must be of type int, string given
A function received a value of the wrong type for a typed parameter.
Warning: Array to string conversion
An array was used where a string is expected — echoing it, concatenating it, or passing it to a string function.
Fatal error: Uncaught TypeError: Unsupported operand types: string + int
An arithmetic or array operator was used with incompatible types (PHP 8 is stricter than PHP 7).
TS2564: Property 'x' has no initializer and is not definitely assigned in the constructor
With strictPropertyInitialization on, a class property declared without ? or a default isn’t set in the constructor.
TS2345: Argument of type 'string | undefined' is not assignable to parameter of type 'string'.
A value’s type doesn’t match the function parameter — commonly a possibly-undefined value passed where a definite one is required.
java.lang.ClassCastException: class A cannot be cast to class B
An object was cast to a type it isn’t.
Swift: The compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions
A long expression (often in a SwiftUI body) has too many possible type combinations for the compiler — or hides a type error.
AttributeError: 'X' object has no attribute 'y'
You accessed an attribute or method that doesn’t exist on that object type.
Fatal error: Uncaught Error: Cannot use object of type stdClass as array
Code used array syntax (`$x['key']`) on an object.
Swift: 'X' is only available in iOS 16.0 or newer
You used an API that requires a newer iOS than your deployment target.
Two steps away (36)
DeprecationWarning: Buffer() is deprecated due to security and usability issues (DEP0005)
Code (yours or a dependency) uses the deprecated new Buffer() constructor.
Deprecated: strlen(): Passing null to parameter #1 ($string) of type string is deprecated
PHP 8.1+ warns when null is passed to a built-in function that expects a string/int.
Deprecated: Creation of dynamic property Foo::$bar is deprecated
PHP 8.2+ deprecates creating properties that aren’t declared in the class.
java.lang.IllegalArgumentException
A method rejected an argument value as invalid.
java.lang.IllegalStateException
A method was called when the object wasn’t in the right state for it.
java.lang.ArithmeticException: / by zero
Integer division or modulo by zero.
PHP Fatal error: Allowed memory size of X bytes exhausted
The script tried to use more memory than PHP’s `memory_limit` allows.
PHP Fatal error: Uncaught Error: Call to undefined function
PHP can’t find the function you called — usually a missing extension, missing include, or namespace issue.
Fatal error: Cannot redeclare function foo() (previously declared in …)
The same function (or class) was defined twice — usually a file included more than once.
TypeError [ERR_INVALID_ARG_TYPE]: The "path" argument must be of type string. Received undefined
A Node API got an argument of the wrong type — usually undefined because an env var or config value is missing.
Warning: Undefined variable $x
PHP read a variable that was never assigned in the current scope.
Composer: PHP Fatal error: Allowed memory size of 1610612736 bytes exhausted
Composer ran out of memory while resolving or installing dependencies.
WordPress on PHP 8: Fatal error: Uncaught Error: Call to undefined function create_function() / each()
An old plugin/theme uses functions removed in PHP 8 (create_function, each), so the site breaks after a PHP upgrade.
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…
TS2322: Type 'X' is not assignable to type 'Y'
You assigned a value whose type doesn’t match the declared type of the variable, property or return value.
TypeError: x is not a constructor
new was used with something that isn’t a class/constructor — usually a wrong import.
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.
TS2304: Cannot find name 'x'.
TypeScript doesn’t know an identifier — a missing import, missing type definitions (e.g. for Node or Jest globals), or a typo.
TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts"
Node tried to run a TypeScript file as ESM without a TypeScript loader.
TS2307: Cannot find module 'x' or its corresponding type declarations.
TypeScript can’t resolve the import — the package isn’t installed, the path alias isn’t configured, or there are no types.
TS2339: Property 'x' does not exist on type 'Y'.
TypeScript’s type for the object doesn’t include that property.
java.lang.StringIndexOutOfBoundsException: begin 0, end 10, length 5
substring()/charAt() used an index outside the string.
java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable)
Code tried to modify an immutable or fixed-size collection.
java.io.IOException: Stream closed
Code read or wrote a stream after it was closed — often by a try-with-resources block or a wrapper closing the underlying stream.
error CS0246: The type or namespace name 'X' could not be found (are you missing a using directive or an assembly reference?)
The compiler doesn’t know the type — missing using, missing NuGet package/project reference, or a target framework mismatch.
error CS0103: The name 'x' does not exist in the current context
The identifier isn’t declared in scope — typo, variable declared in another block, missing using static, or a Razor/partial class…
error CS1061: 'X' does not contain a definition for 'Y' and no accessible extension method 'Y' accepting a first argument of type 'X' could be found
The member you call doesn’t exist on that type — typo, wrong type, missing using for an extension method, or an API removed in a…
TypeError: x is not a function
You called something as a function, but its value is not a function (it’s undefined, a string, an object…).
ImportError: cannot import name 'x' from 'y'
The module was found, but the name you’re importing from it doesn’t exist — usually a version change or a circular import.
KeyError: 'x'
You accessed a dictionary key that doesn’t exist.
Fatal error: Uncaught Error: Call to a member function x() on null
Code called a method on a variable that is null instead of an object.
Fatal error: Uncaught ArgumentCountError: Too few arguments to function foo(), 1 passed and exactly 2 expected
A function was called with fewer arguments than it requires.
Fatal error: Uncaught DivisionByZeroError: Division by zero
Code divided by zero (or used modulo by zero) — PHP 8 throws instead of warning.
Swift: Fatal error: Index out of range
Code accessed an array index that doesn’t exist — empty arrays, off-by-one loops, or data changing while a table reloads.
Swift: Could not cast value of type 'X' to 'Y'
A force cast (as!) failed because the object isn’t the expected type.
Swift: No such module 'X' (module not found)
Xcode can’t find a Swift package, pod or framework you import.
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