rdblue commented on code in PR #17343:
URL: https://github.com/apache/iceberg/pull/17343#discussion_r4169781241
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api/src/main/java/org/apache/iceberg/expressions/Expressions.java:
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@@ -317,6 +319,55 @@ public static <T> UnboundTerm<T> transform(String name,
Transform<?, T> transfor
return new UnboundTransform<>(ref(name), transform);
}
+ /**
+ * Create a reference to a function by identifier, in the catalog of the
referencing object.
+ *
+ * <p>Identifier parts are used as given and are never parsed or split. A
part that contains dots
+ * is a single part, not a namespace followed by a function name.
+ *
+ * @param identifier namespace names followed by the function name
+ * @return a function reference
+ */
+ public static FunctionReference function(String... identifier) {
+ return new FunctionReference(null, Arrays.asList(identifier));
+ }
+
+ /**
+ * Create a reference to a function by identifier, in the catalog of the
referencing object.
+ *
+ * @param identifier namespace names followed by the function name
+ * @return a function reference
+ */
+ public static FunctionReference function(List<String> identifier) {
+ return new FunctionReference(null, identifier);
+ }
+
+ /**
+ * Create a reference to a function in a specific catalog.
+ *
+ * @param catalog a catalog name
+ * @param identifier namespace names followed by the function name
+ * @return a function reference
+ */
+ public static FunctionReference function(String catalog, List<String>
identifier) {
+ return new FunctionReference(catalog, identifier);
+ }
+
+ /**
+ * Create an expression that applies a function to zero or more arguments.
+ *
+ * <p>Each argument must be a value expression ({@link Term}), a predicate
({@link Expression}),
+ * or a constant. Constants are converted to {@link Literal}.
+ *
+ * @param function a function reference
+ * @param arguments value expressions, predicates, or constants passed to
the function
+ * @param <T> the Java type of this term
+ * @return an unbound apply expression
+ */
+ public static <T> UnboundApply<T> apply(FunctionReference function,
List<Object> arguments) {
Review Comment:
The other methods look good, but I think `List<Object>` is too broad here.
This helper may need to be omitted until we have the type hierarchy built out
with a type for `ValueExpression + Predicate`, which I think is called
`FUNC_ARG` in the spec (maybe `FunctionArg` here?).
I think @danielcweeks has been working on the hierarchy changes.
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