shehabgamin commented on issue #14296:
URL: https://github.com/apache/datafusion/issues/14296#issuecomment-2614200125
I like the idea of "user-defined coercion rules" and think we should take it
a step further by striving for a paradigm of "user-defined configurability" in
DataFusion.
Just as SQLParser has `GenericDialect`, which is permissive and
general-purpose, applying a similar principle to components of DataFusion would
provide greater flexibility and adaptability.
Attaching `with_type_coercion_rules` to a `SessionContext` is an interesting
idea, but I worry this approach might not be flexible enough for nuanced
situations. Functions, expressions, and other components often have unique
coercion rules specific to their context or intended use cases. A
one-size-fits-all approach at the `SessionContext` level might not address
these needs, so a more granular mechanism to define and override coercion rules
at a localized scope could be necessary.
For instance, with the built-in UDFs that DataFusion offers, it would be
powerful if users could customize various components of a UDF.
Take the `AsciiFunc` as an example, both of the following signatures could
be valid depending on user requirements:
```
Signature::string(1, Volatility::Immutable)
Signature::coercible(
vec![TypeSignatureClass::Native(logical_string())],
Volatility::Immutable,
)
```
The default implementation of `AsciiFunc` would prioritize being permissive
and general-purpose:
```
impl AsciiFunc {
pub fn new() -> Self {
Self {
signature: Signature::one_of(
vec![
TypeSignature::Coercible(vec![TypeSignatureClass::Native(
logical_string(),
)]),
],
Volatility::Immutable,
),
}
}
}
```
However, what if users could further customize the behavior of `AsciiFunc`
like this?
```
let ascii = AsciiFunc::new()
.with_signature(Signature::string(1, Volatility::Immutable))
// Define other customizations as well
.with_display_name(vec![lit("Meow")])
.with_is_nullable(false)
...
.with_...
...
?;
```
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