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DI: special solution for singletons with private default ctor

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...which declare DependencyFactory as friend.
Yes, we want to encourrage that usage pattern.

Problem is, std::is_constructible<X> gives a misleading result in that case.
We need to do the instantiation check within the scope of DependencyFactory
This commit is contained in:
Fischlurch 2018-03-30 06:48:34 +02:00
parent b3d18c1a74
commit 5d0c2b6d2c
3 changed files with 57 additions and 15 deletions
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20
src/lib/depend2.hpp
View file

@ -187,9 +187,25 @@ namespace lib {
atDestruction ([obj]{ delete obj; });
return obj;
}
// try to instantiate the default ctor
template<class X, typename = decltype(X())>
static std::true_type __try_instantiate(int);
template<class>
static std::false_type __try_instantiate(...);
/** metafunction: can we instantiate the desired object here?
* @remark need to perform the check right here in this scope, because
* default ctor can be private with DependencyFactory declared friend
*/
template<typename X>
struct canDefaultConstruct
: decltype(__try_instantiate<X>(0))
{ };
template<class TAR>
static meta::enable_if<std::is_constructible<TAR>,
static meta::enable_if<canDefaultConstruct<TAR>,
TAR* >
buildInstance()
{
@ -204,7 +220,7 @@ namespace lib {
"Application architecture or lifecycle is seriously broken.");
}
template<class ABS>
static meta::disable_if<std::__or_<std::is_abstract<ABS>,std::is_constructible<ABS>>,
static meta::disable_if<std::__or_<std::is_abstract<ABS>,canDefaultConstruct<ABS>>,
ABS* >
buildInstance()
{

12
tests/library/dependency-configuration-test.cpp
View file

@ -332,6 +332,11 @@ namespace test{
return magic_++;
}
};
// NOTE: the following is rejected due to missing default ctor
DependInject<Dummy<9>>::useSingleton<Veryspecial>();
VERIFY_ERROR (FATAL, Depend<Dummy<9>>{}() );
int backdoor = 22;
@ -358,6 +363,11 @@ namespace test{
{////////////////////////////////////////////////////TEST-Scope
////////////// NOTE: the following does not compile
// // since Veryspecial has no default ctor...
// //
// DependInject<Dum>::Local<Dum> impossible;
DependInject<Dum>::Local<Dum> insidious ([&]{ return new Veryspecial{backdoor}; });
CHECK ((1+5+7+9) == checksum );
@ -378,7 +388,7 @@ namespace test{
CHECK ((1+5+7+9+9) == checksum );
}////////////////////////////////////////////////////(End)TEST-Scope
CHECK ((1+5+7+9) == checksum );
CHECK ((1+5+7+9)*7 == dumm().probe() );
CHECK ( 0 == tricky().probe());

40
wiki/thinkPad.ichthyo.mm
View file

@ -27697,9 +27697,9 @@
</node>
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@ -27772,8 +27772,8 @@
</node>
</node>
</node>
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<icon BUILTIN="button_ok"/>
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<icon BUILTIN="broken-line"/>
@ -27796,30 +27796,46 @@
<node COLOR="#338800" CREATED="1522200189706" ID="ID_302642427" MODIFIED="1522382084962" TEXT="m&#xf6;glichst alle instance-Pointer zur&#xfc;cksetzen">
<icon BUILTIN="button_ok"/>
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<linktarget COLOR="#639d9e" DESTINATION="ID_1152640572" ENDARROW="Default" ENDINCLINATION="-89;0;" ID="Arrow_ID_1512382393" SOURCE="ID_1741501987" STARTARROW="None" STARTINCLINATION="28;-1;"/>
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</node>
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