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digitalmars.D.learn - What is the Utility of Parent Class Method Hiding in Inheritance?

reply Vijay Nayar <madric gmail.com> writes:
https://dlang.org/spec/function.html#function-inheritance

Consider this snippet from the documentation:

class A
{
     int foo(int x) { ... }
     int foo(long y) { ... }
}

class B : A
{
     override int foo(long x) { ... }
}

void test()
{
     B b = new B();
     b.foo(1);  // calls B.foo(long), since A.foo(int) not 
considered
     A a = b;

     a.foo(1);  // issues runtime error (instead of calling 
A.foo(int))
}


I ran into this the other day, where I had a function of the same 
name in a child class, and found that all functions in the parent 
of the same name now became hidden, unless I add an alias 
statement.

After a bit of reading, I understood the rule and how it works, 
but what I'm missing is the "why".  Why is it desirable to hide 
methods from a parent class which have the same name (but 
different arguments) as a method in a class?
Jan 14 2019
next sibling parent ag0aep6g <anonymous example.com> writes:
On 14.01.19 10:10, Vijay Nayar wrote:

 After a bit of reading, I understood the rule and how it works, but what 
 I'm missing is the "why".  Why is it desirable to hide methods from a 
 parent class which have the same name (but different arguments) as a 
 method in a class?


https://dlang.org/articles/hijack.html#derived-class-members
Jan 14 2019
prev sibling parent reply Neia Neutuladh <neia ikeran.org> writes:
On Mon, 14 Jan 2019 09:10:39 +0000, Vijay Nayar wrote:

      a.foo(1);  // issues runtime error (instead of calling
 A.foo(int))


Calling the function doesn't issue any sort of error. Overriding one 
overload without overloading or explicitly aliasing in the rest issues a 
compile-time error.

If you got a runtime error instead, please create a bug report.


 I ran into this the other day, where I had a function of the same name
 in a child class, and found that all functions in the parent of the same
 name now became hidden, unless I add an alias statement.


If the functions from the parent class are hidden but your code compiles, 
please create a bug report.
Jan 14 2019
parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 1/14/19 2:30 PM, Neia Neutuladh wrote:

 On Mon, 14 Jan 2019 09:10:39 +0000, Vijay Nayar wrote:

       a.foo(1);  // issues runtime error (instead of calling
 A.foo(int))


 
 Calling the function doesn't issue any sort of error. Overriding one
 overload without overloading or explicitly aliasing in the rest issues a
 compile-time error.
 
 If you got a runtime error instead, please create a bug report.
 

 I ran into this the other day, where I had a function of the same name
 in a child class, and found that all functions in the parent of the same
 name now became hidden, unless I add an alias statement.


 
 If the functions from the parent class are hidden but your code compiles,
 please create a bug report.
 


Well, for sure, the documentation needs to be updated!

It was 2.068 that removed the HiddenFuncError, and made this a compile 
error instead. If your compiler is that or newer, definitely file a bug 
report.

-Steve
Jan 16 2019
next sibling parent Vijay Nayar <madric gmail.com> writes:
On Wednesday, 16 January 2019 at 17:01:06 UTC, Steven 
Schveighoffer wrote:

 On 1/14/19 2:30 PM, Neia Neutuladh wrote:

 On Mon, 14 Jan 2019 09:10:39 +0000, Vijay Nayar wrote:

       a.foo(1);  // issues runtime error (instead of calling
 A.foo(int))


 
 Calling the function doesn't issue any sort of error. 
 Overriding one
 overload without overloading or explicitly aliasing in the 
 rest issues a
 compile-time error.
 
 If you got a runtime error instead, please create a bug report.
 

 I ran into this the other day, where I had a function of the 
 same name
 in a child class, and found that all functions in the parent 
 of the same
 name now became hidden, unless I add an alias statement.


 
 If the functions from the parent class are hidden but your 
 code compiles,
 please create a bug report.
 


 Well, for sure, the documentation needs to be updated!

 It was 2.068 that removed the HiddenFuncError, and made this a 
 compile error instead. If your compiler is that or newer, 
 definitely file a bug report.

 -Steve


It's a compile error, and it says that one should use alias as 
well.  I was just surprised and I hadn't thought of why this 
alias would be needed.  Based on the recommendation I found the 
language documentation, but there was no link to the article 
explaining the rationale.  But I'm glad I read that article, it 
makes a lot more sense now.
Jan 16 2019
prev sibling parent reply Neia Neutuladh <neia ikeran.org> writes:
On Wed, 16 Jan 2019 12:01:06 -0500, Steven Schveighoffer wrote:

 It was 2.068 that removed the HiddenFuncError, and made this a compile
 error instead. If your compiler is that or newer, definitely file a bug
 report.


Oh god, that must have been awful. I'm glad we're no longer in those 
benighted times.
Jan 16 2019
parent Steven Schveighoffer <schveiguy gmail.com> writes:
On 1/16/19 12:25 PM, Neia Neutuladh wrote:

 On Wed, 16 Jan 2019 12:01:06 -0500, Steven Schveighoffer wrote:

 It was 2.068 that removed the HiddenFuncError, and made this a compile
 error instead. If your compiler is that or newer, definitely file a bug
 report.


 
 Oh god, that must have been awful. I'm glad we're no longer in those
 benighted times.
 


I will never forget those times! This subject was actually my first 
reason for posting to the forums :)

https://forum.dlang.org/post/f8qrgg$12q8$1 digitalmars.com

Good times...

-Steve
Jan 17 2019