findepi commented on issue #11513:
URL: https://github.com/apache/datafusion/issues/11513#issuecomment-2401814374
> ```rust
> pub trait LogicalType {
> fn native(&self) -> &NativeType;
> fn name(&self) -> Option<&str>; // as in 'ARROW:extension:name'.
> }
> ```
@notfilippo This might work. I started similar prototype for
https://github.com/apache/datafusion/issues/12644.
To reliably encode types in Arrow schema, we would need a structured
approach, perhaps something like this
```rust
pub trait Type: Sync + Send {
fn name(&self) -> &Arc<TypeName>;
...
}
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct TypeName {
basename: String,
name: String,
parameters: Vec<TypeParameter>,
}
pub type TypeNameRef = Arc<TypeName>;
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum TypeParameter {
Type(TypeNameRef),
Number(i128),
}
impl TypeName {
pub fn basename(&self) -> &str {
&self.basename
}
pub fn name(&self) -> &str {
&self.name
}
pub fn parameters(&self) -> &[TypeParameter] {
&self.parameters
}
pub fn new(basename: impl Into<String>, parameters: Vec<TypeParameter>)
-> Self {
// TODO assert parses, no braces, etc.
let basename = basename.into();
let name = FormatName {
basename: &basename,
parameters: ¶meters,
}
.to_string();
Self {
basename,
name,
parameters,
}
}
pub fn from_basename(basename: impl Into<String>) -> Self {
Self::new(basename, vec![])
}
}
```
To allow type-checking ("is int" or "is string") for optimizer rules such as
`UnwrapCastExprRewriter` we could use `Any`
```rust
pub trait Type: Sync + Send {
fn as_any(&self) -> &dyn Any;
...
}
```
Type should also describe how to compare (native) values of that type, their
equality, etc.
(for example, per SQL spec, `timestamp with time zone` has interesting
equality defined on part of the value, so bit-by-bit equality cannot be
assumed).
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