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https://issues.apache.org/jira/browse/FLINK-11961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16795997#comment-16795997
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Jark Wu commented on FLINK-11961:
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Hi [~lzljs3620320], it's not to combine {{PlannerExpression}} and
{{CallGenerator}}. It is like a combination of {{PlannerExpression}} and
{{CallGenerator}}.
Similar to {{CallGenerator}}: they have the same responsibility to generate
code for a call. But ExprCodeGen extends that a bit: not just support a call
but also other expressions such as {{LiteralCodeGen}}, {{FieldAccessCodeGen}}.
Similar to {{PlannerExpression}}: they have the same Inheritance structure,
e.g. the base classes {{BinaryExprCodeGen}}, {{UnaryExprCodeGen}} and concrete
classes for every functions/operators code generation {{ConcatCodeGen}},
{{LikeCodeGen}}, {{PlusCodeGen}}.
> Clear up and refactor the code generation of scalar functions and operators
> ---------------------------------------------------------------------------
>
> Key: FLINK-11961
> URL: https://issues.apache.org/jira/browse/FLINK-11961
> Project: Flink
> Issue Type: Improvement
> Components: SQL / Planner
> Reporter: Jark Wu
> Assignee: Jark Wu
> Priority: Major
>
> Currently, the code generation of scalar functions and operators are complex
> and messy.
> There are several ways to support codegen for a function/operator:
> (1) Implement {{generate...}} in {{ScalarOperatorGens}} and invoke it in the
> big match pattern of {{ExprCodeGenerator}}.
> (2) Implement a {{CallGenerator}} and add it to {{FunctionGenerator}}.
> (3) Implement a util method and add it to {{BuiltinMethods}} and
> {{FunctionGenerator}}.
> It will confuse developer which is the most efficient way to implement a
> function.
> In this issue, we will propose a unified way to code generate
> functions/operators.
> Some initial idea:
> 1. Introduce an {{ExprCodeGen}} interface, and all the function/operators
> code generator should extend this to implement the {{codegen}} method. It's
> like a combination of {{PlannerExpression}} and {{CallGenerator}}.
> 2. Rename {{ExprCodeGenerator}} to {{RexCodeGenerator}}.
> 3. Use a big match pattern to mapping {{RexCall}} to specific {{ExprCodeGen}}
> {code:scala}
> trait ExprCodeGen {
> def operands: Seq[GeneratedExpression]
> def resultType: InternalType
> def codegen(ctx: CodeGeneratorContext): GeneratedExpression
> }
> case class ConcatCodeGen(operands: Seq[GeneratedExpression]) extends
> ExprCodeGen {
> override def resultType: InternalType = InternalTypes.STRING
> override def codegen(ctx: CodeGeneratorContext): GeneratedExpression = {
> nullSafeCodeGen(ctx) {
> terms => s"$BINARY_STRING.concat(${terms.mkString(", ")})"
> }
> }
> }
> {code}
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