bevyengine/bevy · error · ArgError

expected an argument but received none

Error message

expected an argument but received none

What it means

Occurs when an empty ArgList is accessed: the caller attempts to retrieve or parse an argument when no arguments remain. It is the empty-list guard for reflected function argument access, meaning the function was invoked (or its args inspected) with fewer arguments than the code tried to read.

Source

Thrown at crates/bevy_reflect/src/func/args/error.rs:35

        /// Expected argument type path.
        expected: Cow<'static, str>,
        /// Received argument type path.
        received: Cow<'static, str>,
    },
    /// The argument has the wrong ownership.
    #[error("expected {expected} value but received {received} value (@ argument index {index})")]
    InvalidOwnership {
        /// Argument index.
        index: usize,
        /// Expected ownership.
        expected: Ownership,
        /// Received ownership.
        received: Ownership,
    },
    /// Occurs when attempting to access an argument from an empty [`ArgList`].
    ///
    /// [`ArgList`]: crate::func::args::ArgList
    #[error("expected an argument but received none")]
    EmptyArgList,
}

/// The given argument count is out of bounds.
#[derive(Debug, Error, PartialEq)]
#[error("argument count out of bounds: {0}")]
pub struct ArgCountOutOfBoundsError(pub usize);

View on GitHub (pinned to 396ca72708)

Solutions

1. Provide the arguments required by the function's signature
2. Check the ArgList length before calling

When it happens

Trigger: Thrown at crates/bevy_reflect/src/func/args/error.rs:35 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/fdeee637487c22d3. Report an issue: GitHub.