Today I came across a situation which brought it home to me again\u00a0how (in my opinion) C++ could desperately do with native lambda function support.\u00a0 The standard library has introduced a load of great algorithms, but providing predicates and the like to them is a real pain – and I think that\u00a0because of this\u00a0people tend to stick to hand rolling good old-fashioned loops.<\/p>\n
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Consider replacing a few different characters in a std::string with a single given character, e.g., replace the characters ‘$’\u00a0and\u00a0‘|’ with ‘_’.\u00a0 A good way of doing this in C++ would be to use the boost regular expression library, but we could also use the std::replace_if() algorithm.\u00a0 All we have to do to use this algorithm is to privide a predicate that indicates if a given character should be replaced or not (say called is_bad_char()), then we do something like:<\/p>\n
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[code lang=\"cpp\"] replace_if(str.begin(), str.end(), is_bad_char(), '_'); [\/code]<\/pre>\n\u00a0Looks easy enough, and it’s nice and concise.\u00a0 All we have to do now is define is_bad_char(), something like:<\/p>\n
[code lang=\"cpp\"]\r\nstruct is_bad_char: public std::unary_function\r\n{\r\n bool operator() (const char& c) const\r\n {\r\n return !(c == '$' || c == '|');\r\n }\r\n};\r\n[\/code]<\/pre>\nI mean! what a pallava!\u00a0\u00a0that’s quite a mouthful, would you really be bothered? You would have a loop coded in just the time it took to start to remember that syntax, never mind the typing. it also looks terribly inelegant.<\/p>\n
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Now when native lambda support arrvies we will be able to do something like this instead:<\/p>\n
[code lang=\"cpp\"]\r\nreplace_if(str.begin(), str.end(),\r\n <>(char c) -> bool { return !(c == '$' || c == '|'); },\r\n '_');\r\n[\/code]<\/pre>\nThat’s much better… but not available yet, we will just have to wait for c++0x to arrive. In the mean time I will just have to use lambdas in the many other languages that support them and\u00a0pine when using C++.<\/p>\n","protected":false},"excerpt":{"rendered":"
Today I came across a situation which brought it home to me again\u00a0how (in my opinion) C++ could desperately do with native lambda function support.\u00a0 The standard library has introduced a load of great algorithms, but providing predicates and the like to them is a real pain – and I think that\u00a0because of this\u00a0people tend […]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[13,11,12],"class_list":["post-54","post","type-post","status-publish","format-standard","hentry","category-tech-stuff","tag-algorithm","tag-cplusplus","tag-lambda-expression"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t