.net - C++/CLI good coding practice, Indexed properties if-check or try..catch? -

a rather short , simple question.

let's use piece of code:

public ref class foo { private:     system::collections::generic::dictionary<system::string ^,system::string ^> ^ adictionary;  public:      property system::string ^ someindexedproperty[system::string ^]     {     public: system::string ^ get(system::string ^ index)             {                 return adictionary[index];             }     }  public:     foo(void)     {         adictionary = gcnew system::collections::generic::dictionary<system::string ^,system::string ^>();     } }; 

would better surround/pre-check return if statement ( if( adictionary->containskey(index) ) or better surround return statement try..catch block?

in both cases returning nullptr when fail.

speed not of issue. general "this better reason" suffice.

i firmly believe if there legal condition reasonably allow, should not catch exception detect it. in other words, use if statement. akin letting loops on arrays run out until arrayindexofboundsexception , try...catch oblivion.

on related note, might make sense property throw keynotfoundexception instead o returning null. callers might take null , try dereference it, shifts focus , makes harder find bug.