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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
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
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
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
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
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
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