jayzhan211 commented on issue #10507:
URL: https://github.com/apache/datafusion/issues/10507#issuecomment-2275292135
Signature does 3 things
1. Length check
2. Type check
3. Coercion
For length,
the common length check are
1. Exact number
2. Variadic (Any number)
3. VariadicNonZero (Any number but at least one)
4. VariadicEven (Less common, i.e. Map)
For types,
We have two style, Exact and Coercion. Exact rejects if the type mismatch,
Coercion rejects if teh type is not coercible to the target type.
The combination of these are
* `Uniform(Vec<DataType>)` // Exact Number with Exact type
* `UniformCoercion(Vec<DataType>)` // Exact Number with coercion
* `Variadic(DataType)`
* `VariadicCoercion(DataType)`
...
For non-uniform length and more then on data type signature, we could use
`UserDefined`.
The more tricky part is the DataType. We have many functions expect Numeric
type that includes integer, float, ....
For function that expects string, there are Utf8, LargeUtf8, Utf8View.
For type checking, it would be nice to have more general Enum that includes
more than one DataType to check against with.
```rust
enum FunctionType {
Numeric
Integer
Float
...
}
```
Now, we have
```rust
* `Uniform(Vec<FunctionType>)` // Exact Number with Exact type
* `UniformCoercion(Vec<FunctionType>)` // Exact Number with coercion
* `Variadic(FunctionType)`
* `VariadicCoercion(FunctionType)`
```
TypeSignature::Numeric is one of the idea that comes out from it.
For other kinds of complex type check or length check, we fall back to
`UserDefined`
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