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<div class="moz-cite-prefix">Am 26.04.2020 um 14:01 schrieb Benito
van der Zander:<br>
</div>
<blockquote type="cite"
cite="mid:01b0729e-bc34-30e7-32e5-c13e32ef1f83@benibela.de">
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<div id="smartTemplate4-template">Hi,<br>
<br>
<p>perhaps it could be used to merge specializations (if fpc
cannot do that on its own):<br>
</p>
</div>
<div>Like when you have a hashmap THashMap<Key,Value>, and
need three specializations:</div>
<div><br>
</div>
<div>THashMap<string, pointer></div>
<div><br>
</div>
<div>THashMap<string, TObject></div>
<div><br>
</div>
<div>THashMap<string, sizeint></div>
<div><br>
</div>
<div>It is basically three times the same hashmap, but if fpc does
not detect that, it might generate three times the same assembly
code, which waste a lot of space.</div>
<div><br>
</div>
<div><br>
</div>
<div>But with constants it can be merged to TBaseHashMap<Key,
ValueSize: integer> and then you only have one map in the
assembly code, and three wrappers to remove the casting:<br>
</div>
<div><br>
</div>
<div>
<div>THashMap<string, pointer> = TBaseHashMap<string,
sizeof(pointer) > = TBaseHashMap<string, 8 > </div>
<div><br>
</div>
<div>THashMap<string, TObject> = TBaseHashMap<string,
sizeof(TObject) > = TBaseHashMap<string, 8 > <br>
</div>
<div><br>
</div>
<div>THashMap<string, sizeint> = TBaseHashMap<string,
sizeof(sizeint) > = TBaseHashMap<string, 8 > <br>
</div>
<div><br>
</div>
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</blockquote>
<br>
It's not that simple. In principle you're right that the compiler
could try to merge more implementations, but this does not depend on
the declaration of the generic, but the use of the parameter types.<br>
<br>
Take the following example:<br>
<br>
=== code begin ===<br>
<br>
{$mode objfpc}<br>
<br>
type<br>
generic TTest<T> = class<br>
procedure DoSomething;<br>
end;<br>
<br>
TMyClass1 = class<br>
procedure Foobar;<br>
end;<br>
<br>
TMyClass2 = class<br>
procedure Foobar; virtual;<br>
end;<br>
<br>
procedure TTest.DoSomething;<br>
var<br>
o: T;<br>
begin<br>
o.Foobar;<br>
end;<br>
<br>
procedure TMyClass1.Foobar;<br>
begin<br>
Writeln('TMyClass1.Foobar');<br>
end;<br>
<br>
procedure TMyClass2.Foobar;<br>
begin<br>
Writeln('TMyClass2.Foobar');<br>
end;<br>
<br>
type<br>
TTestMyClass1 = specialize TTest<TMyClass1>;<br>
TTestMyClass2 = specialize TTest<TMyClass2>;<br>
<br>
begin<br>
end.<br>
<br>
=== code end ===<br>
<br>
In case of TMyClass1 this will result in a static call to
TMyClass1.Foobar, however in case of TMyClass2 this will result in
an indirect call through the VMT.<br>
<br>
The type information needs to be correct as well, even more so once
we have support for Extended RTTI where one can enumerate
non-published fields, properties and methods in addition to
published. <br>
<br>
Not to mention that your TBaseHashMap would not work with managed
types...<br>
<br>
Regards,<br>
Sven<br>
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