Ichthyostega
fa6ba76f85
As it turns out, using the functional-notation form conversion with *parentheses* will fall back on a C-style (wild, re-interpret) cast when the target type is *not* a class. As in the case in question here, where it is a const& to a class. To the contrary, using *curly braces* will always attempt to go through a constructor, and thus fail as expected, when there is no conversion path available. I wasn't aware of that pitfall. I noticed it since the recently introduced class TimelineGui lacked a conversion operator to BareEntryID const& and just happily used the TimelineGui object itself and did a reinterpret_cast into BareEntryID
103 lines
3.5 KiB
C++
103 lines
3.5 KiB
C++
/* try.cpp - for trying out some language features....
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* scons will create the binary bin/try
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*
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*/
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// 8/07 - how to control NOBUG??
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// execute with NOBUG_LOG='ttt:TRACE' bin/try
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// 1/08 - working out a static initialisation problem for Visitor (Tag creation)
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// 1/08 - check 64bit longs
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// 4/08 - comparison operators on shared_ptr<Asset>
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// 4/08 - conversions on the value_type used for boost::any
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// 5/08 - how to guard a downcasting access, so it is compiled in only if the involved types are convertible
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// 7/08 - combining partial specialisation and subclasses
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// 10/8 - abusing the STL containers to hold noncopyable values
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// 6/09 - investigating how to build a mixin template providing an operator bool()
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// 12/9 - tracking down a strange "warning: type qualifiers ignored on function return type"
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// 1/10 - can we determine at compile time the presence of a certain function (for duck-typing)?
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// 4/10 - pretty printing STL containers with python enabled GDB?
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// 1/11 - exploring numeric limits
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// 1/11 - integer floor and wrap operation(s)
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// 1/11 - how to fetch the path of the own executable -- at least under Linux?
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// 10/11 - simple demo using a pointer and a struct
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// 11/11 - using the boost random number generator(s)
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// 12/11 - how to detect if string conversion is possible?
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// 1/12 - is partial application of member functions possible?
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// 5/14 - c++11 transition: detect empty function object
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// 7/14 - c++11 transition: std hash function vs. boost hash
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// 9/14 - variadic templates and perfect forwarding
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// 11/14 - pointer to member functions and name mangling
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// 8/15 - Segfault when loading into GDB (on Debian/Jessie 64bit
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// 8/15 - generalising the Variant::Visitor
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// 1/16 - generic to-string conversion for ostream
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// 1/16 - build tuple from runtime-typed variant container
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// 3/17 - generic function signature traits, including support for Lambdas
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// 9/17 - manipulate variadic templates to treat varargs in several chunks
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// 11/17 - metaprogramming to detect the presence of extension points
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// 11/17 - detect generic lambda
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// 12/17 - investigate SFINAE failure. Reason was indirect use while in template instantiation
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// 03/18 - Dependency Injection / Singleton initialisation / double checked locking
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// 04/18 - investigate construction of static template members
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// 08/18 - Segfault when compiling some regular expressions for EventLog search
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// 10/18 - investigate insidious reinterpret cast
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/** @file try.cpp
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* Document an insidious wild cast, caused by the syntax `Type(arg)`.
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* I was under the wrong assumption this would be handled equivalent to a constructor invocation.
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* Seemingly it is rather handled as a C-style cast, i.e. equivalent to `(Type)arg`.
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* @see [Question on Stackoverflow](https://stackoverflow.com/q/52782967/444796)
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*/
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typedef unsigned int uint;
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#include "lib/format-cout.hpp"
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#include "lib/test/test-helper.hpp"
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#include "lib/util.hpp"
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#include <string>
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using std::string;
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using util::isSameObject;
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#define SHOW_TYPE(_TY_) \
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cout << "typeof( " << STRINGIFY(_TY_) << " )= " << lib::meta::typeStr<_TY_>() <<endl;
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#define SHOW_EXPR(_XX_) \
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cout << "Probe " << STRINGIFY(_XX_) << " ? = " << _XX_ <<endl;
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class Wau
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{
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int i = -1;
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};
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class Miau
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{
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public:
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uint u = 1;
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};
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int
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main (int, char**)
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{
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Wau wau;
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using ID = Miau &;
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ID wuff = ID(wau);
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cout << "Miau=" << wuff.u
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<< " ref to same object: " << isSameObject (wau, wuff)
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<< endl;
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cout << "\n.gulp.\n";
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return 0;
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}
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