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digitalmars.D.learn - Access outer member of struct from inner struct

reply Andrey <saasecondbox yandex.ru> writes:
Hello,
In this example how can I access the members "read" and "q" of 
struct Outer from Inner struct?
 struct Outer
 {
 	ulong q = 1;
     Inner inner;
 
     void read(ulong value)
     {
         q += value;
     }
 
     void run()
     {
     	q.writeln;
         read(5);
     }
 
     struct Inner
     {
      	void write(string text)
         {
             read(text.length);
             writeln(q);
         }
     }
 }
 
 void main()
 {
     Outer ttt;
     ttt.run();
 }
During compilation I get:
 onlineapp.d(55): Error: this for read needs to be type Outer 
 not type Inner
 onlineapp.d(56): Error: need this for q of type ulong
Apr 02
parent reply Q. Schroll <qs.il.paperinik gmail.com> writes:
On Tuesday, 2 April 2019 at 18:20:09 UTC, Andrey wrote:
 Hello,
 In this example how can I access the members "read" and "q" of 
 struct Outer from Inner struct?
 struct Outer
 {
 	ulong q = 1;
     Inner inner;
 
     void read(ulong value)
     {
         q += value;
     }
 
     void run()
     {
     	q.writeln;
         read(5);
     }
 
     struct Inner
     {
      	void write(string text)
         {
             read(text.length);
             writeln(q);
         }
     }
 }
 
 void main()
 {
     Outer ttt;
     ttt.run();
 }
During compilation I get:
 onlineapp.d(55): Error: this for read needs to be type Outer 
 not type Inner
 onlineapp.d(56): Error: need this for q of type ulong
After removing the calls to writeln, the error I get is:
 `this` for `read` needs to be type `Outer` not type `Inner`
You cannot access stuff in Outer because Inner objects are not outer objects and don't implicitly own an Outer object. In your Inner method `write`, there is no Outer object present at all to call the method on.
Apr 02
parent reply Jacob Carlborg <doob me.com> writes:
On 2019-04-02 20:44, Q. Schroll wrote:

 After removing the calls to writeln, the error I get is:
 
 `this` for `read` needs to be type `Outer` not type `Inner`
You cannot access stuff in Outer because Inner objects are not outer objects and don't implicitly own an Outer object. In your Inner method `write`, there is no Outer object present at all to call the method on.
It works if the struct is nested inside a function [1]. I thought it would work nested inside a struct too. [1] https://dlang.org/spec/struct.html#nested -- /Jacob Carlborg
Apr 02
parent Q. Schroll <qs.il.paperinik gmail.com> writes:
On Tuesday, 2 April 2019 at 18:52:07 UTC, Jacob Carlborg wrote:
 On 2019-04-02 20:44, Q. Schroll wrote:

 After removing the calls to writeln, the error I get is:
 
 `this` for `read` needs to be type `Outer` not type `Inner`
You cannot access stuff in Outer because Inner objects are not outer objects and don't implicitly own an Outer object. In your Inner method `write`, there is no Outer object present at all to call the method on.
It works if the struct is nested inside a function [1]. I thought it would work nested inside a struct too. [1] https://dlang.org/spec/struct.html#nested
The reason it works inside a function is that the struct has a hidden pointer to the function context. The function's local values actually exist when an object of that struct type is being instantiated. The main difference between a struct nested in a function and one inside another struct is that the one in a function cannot┬╣ be created outside of that function while constructing the latter is possible the way you think it is: Outer.Inner innerObj = Outer.Inner(parameters); ┬╣ You can using reflection and stuff like that, but it's still broken if it uses the context.
Apr 02