153 lines
4.1 KiB
Plaintext
153 lines
4.1 KiB
Plaintext
:toc:
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= 自定义语法元素
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本节系统梳理在 QLExpress4 在自定义语法元素方面的接口和能力。
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== 总览
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* 自定义函数
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** 实现CustomFunction接口
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** 使用 Java 函数式接口
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** 通过注解扫描注册
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** 通过QLExpress脚本添加
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** 实现QLFunctionalVarargs
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* 自定义操作符
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** 实现CustomBinaryOperator
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** 替换内置操作符
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** 使用 Java 函数式接口
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** 添加别名
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** 实现QLFunctionalVarargs
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* 扩展函数
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** 继承ExtensionFunction
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** 实现QLFunctionalVarargs
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* 操作符与函数别名
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== 自定义函数
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=== 实现CustomFunction接口
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/test/function/HelloFunction.java[]
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----
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=customComplexFunction]
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----
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=== 使用 Java 函数式接口
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=addFunctionWithJavaFunctional]
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----
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=== 注解方式注册
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=annoObj]
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----
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=addFunctionByAnnotationObject]
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----
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=== 通过QLExpress脚本添加
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=joinFunctionVarargsObj]
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----
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=== 实现QLFunctionalVarargs
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=addFunctionByVarargs]
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----
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=addFunctionByVarargs]
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----
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== 自定义操作符
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=== 实现CustomBinaryOperator并设置优先级
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=addOperatorWithPrecedence]
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----
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=== 替换内置操作符
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=replaceDefaultOperator]
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----
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=== 使用 Java 函数式接口
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=addOperatorBiFunction]
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----
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=== 实现QLFunctionalVarargs
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=addOperatorByVarargs]
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----
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== 扩展函数
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=== 继承ExtensionFunction
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=defineExtensionFunctionByExtensionFunction]
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----
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=== 实现QLFunctionalVarargs
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=defineExtensionFunctionByQLFunctionalVarargs]
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----
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== QLFunctionalVarargs：一个对象同时定义三类操作
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同一个QLFunctionalVarargs对象可同时用作函数、操作符与扩展函数的实现，便于在多处复用统一的语义与实现。该能力来源于接口的可变参数设计，详见下方示例与接口定义。背景讨论参考 link:https://github.com/alibaba/QLExpress/issues/407[issue407]：
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/docs/CustomItemsDocTest.java[tag=qlfunctionalvarargsAllInOne]
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----
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=== 接口定义
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[source,java,indent=0]
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----
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include::../src/main/java/com/alibaba/qlexpress4/api/QLFunctionalVarargs.java[]
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----
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== 操作符与函数别名（亦支持关键字别名）
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[source,java,indent=0]
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----
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include::../src/test/java/com/alibaba/qlexpress4/Express4RunnerTest.java[tag=addAlias]
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----
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== 说明与建议
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- QLFunctionalVarargs 的定义模式下，扩展函数调用时实参列表首位是接收者对象，其后为调用参数；函数与操作符不含接收者。
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- 自定义操作符的优先级需根据表达式期望进行设置，避免与已有运算规则产生混淆。
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- 注解方式注册仅会处理公开方法，且重复名称将注册失败；批量注册返回结果中包含成功与失败清单。
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