Problems encountered after a "struct" is regarded as a property

When I regard a "struct" as an attribute in the class, I can directly read the struct members in practice, but cannot write them directly...

The following is a small exercise:

Unit unit1; interfaceuses winapi. windows, winapi. messages, system. sysutils, system. variants, system. classes, VCL. graphics, VCL. controls, VCL. forms, VCL. dialogs, VCL. struct; Type tform1 = Class (tform) button1: tbutton; button2: tbutton; button3: tbutton; button4: tbutton; button5: tbutton; Procedure button1click (Sender: tobject ); procedure button2click (Sender: tobject); Procedure button4click (Sender: tobject); Procedure button3click (Sender: tobject); Procedure button5click (Sender: tobject); end; tmyclass = Class strict private FPOs: tpoint; Procedure setpos (const value: tpoint); Public Property pos: tpoint read FPOs write setpos; // attribute POS corresponds to a point structure end; vaR form1: tform1; implementation {$ R *. DFM} {tmyclass} procedure tmyclass. setpos (const value: tpoint); begin FPOs: = value; end; {test} procedure tform1.button1click (Sender: tobject); var OBJ: tmyclass; begin OBJ: = tmyclass. create; showmessagefmt ('% d, % d', [obj. POS. x, obj. POS. y]); // you can directly access the elements in the structure. // obj. POS. x: = 11; // but the element in the structure cannot be directly assigned a value. // obj. POS. y: = 22; obj. free; end; // change to procedure tform1.button2click (Sender: tobject); var OBJ: tmyclass; begin OBJ: = tmyclass. create; obj. POs: = point (22, 33); // showmessagefmt ('% d, % d', [obj. POS. x, obj. POS. y]); obj. free; end; // work und 2. Procedure tform1.button3click (Sender: tobject); var OBJ: tmyclass; Pt: tpoint; begin OBJ: = tmyclass. create; PT. x: = 33; PT. y: = 44; obj. POs: = pt; showmessagefmt ('% d, % d', [obj. POS. x, obj. POS. y]); obj. free; end; // work 3 (if the get attribute is not a method) Procedure tform1.button4click (Sender: tobject); var OBJ: tmyclass; P: Ppoint; begin OBJ: = tmyclass. create; P: = ADDR (obj. pos); p. x: = 44; p. y: = 55; showmessagefmt ('% d, % d', [obj. POS. x, obj. POS. y]); obj. free; end; // work und 4 (if the get attribute is not a method) Procedure tform1.button5click (Sender: tobject); var OBJ: tmyclass; begin OBJ: = tmyclass. create; Ppoint (ADDR (obj. pos )). x: = 55; Ppoint (ADDR (obj. pos )). y: = 66; showmessagefmt ('% d, % d', [obj. POS. x, obj. POS. y]); obj. free; end.

Exercise 2:

Unit unit1; interfaceuses winapi. windows, winapi. messages, system. sysutils, system. variants, system. classes, VCL. graphics, VCL. controls, VCL. forms, VCL. dialogs; Type tform1 = Class (tform) Procedure formcreate (Sender: tobject); end; tmyclass = class private FPOs: tpoint; function getpos: tpoint; Procedure setpos (const value: tpoint); function getxy (const index: integer): integer; Procedure setxy (const index, value: integer); Public Property pos: tpoint read getpos write setpos; property X: integer index 0 read getxy write setxy; property Y: integer Index 1 read getxy write setxy; end; var form1: tform1; implementation {$ R *. DFM} {tmyclass} function tmyclass. getpos: tpoint; begin result: = FPOs; end; Procedure tmyclass. setpos (const value: tpoint); begin FPOs: = value; end; function tmyclass. getxy (const index: integer): integer; begin result: = 0; case index of 0: Result: = FPOs. x; 1: Result: = FPOs. y; end; Procedure tmyclass. setxy (const index, value: integer); begin case index of 0: FPOs. x: = value; 1: FPOs. y: = value; end; {test} procedure tform1.formcreate (Sender: tobject); var OBJ: tmyclass; begin OBJ: = tmyclass. create; obj. x: = 11; obj. y: = 22; showmessagefmt ('% d, % d', [obj. POS. x, obj. POS. y]); obj. free; end.