Understanding Rust Error E0087: Too Many Type Arguments

Introduction to Rust Error E0087

Rust Error E0087 occurs when too many type arguments are supplied to a function, and the number of provided type arguments does not match the number of type parameters defined within the function. Although this error code is no longer emitted by the compiler, understanding the issue can help you avoid similar problems in your Rust programming.

Example of Rust Error E0087

Let's look at a simple example that demonstrates Rust Error E0087.

fn foo<T>() {}

fn main() {
    foo::<f64, bool>(); // error: wrong number of type arguments:
                        //        expected 1, found 2
}

Here, the function 'foo' has been defined with a single type parameter 'T'. However, in the 'main' function, we attempt to call 'foo' using two type arguments instead - 'f64' and 'bool'. This mismatch in the number of type arguments provided triggers Rust Error E0087.

How to Fix Rust Error E0087

To resolve Rust Error E0087, ensure the number of supplied type arguments matches the number of type parameters defined in the function. In our example, we need to modify the call to 'foo' in the 'main' function by providing only one type argument, as follows:

fn main() {
    foo::<f64>(); // No error
}

By providing the correct number of type arguments, we eliminate Rust Error E0087, and the code can compile and run successfully.