Simplify variable #2647
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Simplify variable #2647
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It seems using dynamic_cast is simpler.
reyoung
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wangkuiyi
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Jun 29, 2017
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This PR obviously complicated Variable; instead of simplifying it.
dynamic_cast is not necessary here, because we don't implement polymorphism using virtual functions and class derivation. Instead, we are using template. This allows us to know type T at compile time and to use static_cast.
https://stackoverflow.com/questions/579887/how-expensive-is-rtti shows how much more expensive dynamic_cast is, compared with static_cast. That is why I designed Variable's Placeholder to use template and static_cast.
| @@ -25,42 +25,37 @@ class Variable { | |||
| public: | |||
| template <typename T> | |||
| const T& Get() const { | |||
| PADDLE_ASSERT(IsType<T>()); | |||
| return *static_cast<const T*>(holder_->Ptr()); | |||
| auto holder = dynamic_cast<PlaceholderImpl<T>*>(holder_.get()); | |||
|
Please don't be frustrated because I closed this PR. It is always a great trial to shave something with the Occam's Razor! @reyoung |
heavengate
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It seems that
Placeholder::PtrandPlaceholder::Typedoes not need. We can use dynamic_cast to achieve the same goal and make implementation simpler.