在我们实际的ABAP开发中，我们经常会使用动态编程，如动态地获取运行参数，动态创建类型、内表等等。这样做给我们带来的好处之一，就是“扩充”了我们代码的重用性。
一.动态编程（Field Symbol以及casting）
以field symbol为例:
*&———————————————————————* *& Report ZTEST_FIELD_SYMBOL *& Tang Can *&———————————————————————* *& Test Field symbo *&———————————————————————* REPORT ZTEST_FIELD_SYMBOL. * define my teype TYPES: typ_mine(10) type c. * define Data type DATA: smallfield(5) type c, largefield(15) type c VALUE ‘123456789012345′, typename(8) type c value ‘TYP_MINE’, sometype type REF TO CL_ABAP_TYPEDESCR, rrt_type TYPE REF TO CL_ABAP_DATADESCR. FIELD-SYMBOLS: <any> TYPE any, <mine> type typ_mine. * type==>type ASSIGN largefield to <mine> CASTING. WRITE:/ ‘Casting from 15==>10 to <mine>:’, <mine>. ASSIGN largefield to <any> CASTING type typ_mine. WRITE:/ ‘Casting from 15==>10 to <any>,”Casting type to typ_mine” in Field-symbol:’, <any>. ASSIGN largefield to <any> CASTING type n. WRITE:/ ‘Casting from 15==>n to <any>,”Casting type to N” in Field-symbol:’, <any>. ASSIGN largefield to <any> CASTING type (typename). WRITE:/ ‘Casting from 15==>10 to <any>,”Dynamically Casting type to typ_mine” in Field-symbol:’, <any>. sometype = cl_abap_typedescr=>DESCRIBE_BY_NAME( ‘TYP_MINE’ ). “ASSIGN largefield to <any> CASTING TYPE HANDLE sometype. rrt_type ?= sometype. ASSIGN largefield to <any> CASTING TYPE HANDLE rrt_type. WRITE:/ ‘Casting from 15==>10 to <any>,”using CL_ABAP_TYPEDESCR” in Field-symbol:’, <any>. ASSIGN largefield to <any> CASTING LIKE smallfield. WRITE:/ ‘Casting from 15==>5 to <any>,”Like Smallfield” in Field-symbol:’, <any>. ASSIGN largefield to <any> CASTING LIKE <mine>. WRITE:/ ‘Casting from 15==>5 to <any>,”Like <mine>” in Field-symbol:’, <any>.
测试程序，我们的运行结果：
二.动态编程（五类Token分类）
1.Dynamic Field Specification
原理：
测试程序：
*&———————————————————————* *& Report ZTEST_DYN_FIELD *& test Dynamically field-specification *&———————————————————————* REPORT ZTEST_DYN_FIELD. * constance CONSTANTS: a type i value 1, b type i value 2. * data DATA: name(5) TYPE c. FIELD-SYMBOLS: <lfs> type i. * test name = ‘A’. ASSIGN (name) to <lfs>. write:/10 <lfs>. * test name = ‘B’. ASSIGN (name) to <lfs>. write:/10 <lfs>.
结果：
2.Dynamic Type Specification
原理：
实现：
上面第一点已经总结。
3.Dynamic Component Specification
原理：
4.Dynamic Clause Specification
原理：
5.Dynamic Subroutine Specification
原理：
6.总结
测试dynamic field specification，dynamic Type Specification, dynamic Component Specification, Dynamic Clause specification：
测试程序:
*&———————————————————————* *& Report ZTEST_DYN *&—————————————————————–* REPORT ZTEST_DYN. DATA: ref_data type REF TO data, “for creating internal table itab_cond type TABLE OF string, “for condition lw_name type string. “for write FIELD-SYMBOLS: <lfs_st> type ANY, <lfs_field> type any. PARAMETERS: p_tab_nm type string, p_cond type string. * create the internal-table of Parameter CREATE DATA ref_data type (p_tab_nm). ASSIGN ref_data->* to <lfs_st>. append p_cond to itab_cond. * get the data of dynamic table SELECT * from (p_tab_nm) into <lfs_st> UP TO 1 ROWS where (itab_cond). ENDSELECT. * write write:/10 ‘Using ”Component Name” to output’. lw_name = ‘CARRID’. ASSIGN COMPONENT lw_name OF STRUCTURE <lfs_st> to <lfs_field>. write:/10 lw_name, 30 <lfs_field>. lw_name = ‘CONNID’. ASSIGN COMPONENT lw_name OF STRUCTURE <lfs_st> to <lfs_field>. write:/10 lw_name, 30 <lfs_field>. lw_name = ‘TEXT’. ASSIGN COMPONENT lw_name OF STRUCTURE <lfs_st> to <lfs_field>. write:/10 lw_name, 30 <lfs_field>. write:/10 ‘———————————————’. write:/10 ‘Using ”Indext” to output’. ASSIGN COMPONENT 1 OF STRUCTURE <lfs_st> to <lfs_field>. write:/10 ‘Index 1′, 30 <lfs_field>. ASSIGN COMPONENT 2 OF STRUCTURE <lfs_st> to <lfs_field>. write:/10 ‘Index 2′, 30 <lfs_field>. ASSIGN COMPONENT 3 OF STRUCTURE <lfs_st> to <lfs_field>. write:/10 ‘Index 3′, 30 <lfs_field>.
结果：
画面输出：
结果：
