expression

问题 This question already has answers here : What specifically are the dangers of eval(parse(…))? (4 answers) Closed 6 years ago . I've been told that it is a bad habit to parse and evaluate a character string to_run = "for (i in 1:10){print(i);print('Hello World!')}" eval(parse(text=to_run)) Why is it a bad habit? It seems to me to be quite a flexible way of programming as we can construct our code in a iterative manner by pasting character strings together. For example it allows to easily deal

问题 I am struggling with a date calculation to define my own range for a bar chart series. My dynamic dates are parameters the timestamp parameters "timestamp1", "timestamp2", "timestamp3", "timestamp4" wheras I want to create the intervals interval1: days between "timestamp1" and "timestamp2" interval2: days between "timestamp3" and "timestamp4". What is the expression that I have to add to my variables in order to have two time intervals for my bar chart series? I am completely lost with this

问题 Im having problems building a query with the linq to sql data query expression in c#. What I'm trying to ultimately do is based on this pseudo-code expression. public IQueryable<CTest> searchRecords(string category, string searchString, DateTime startDate, DateTime endDate, int searchType, int searchType2) { //-Search All Records //-From the information table //-By the category column containing a specific search //-Also by // ~if both a startDate and endDate are entered (not (0000,00,00) OR

问题 In one of the C++ modules we have, we have an expression evaluation language. \ EVDataElement NAME::eval( const EvalContext &ec, \ const bool recursiveFlag, \ EVEvaluatorTraceFormatter * trace ) \ { \ /* EVTimer timer("(DECLARE_REL_EVAL)","eval","*", "", 1,1, 3); */ \ EVDataElement val ( \ (left->eval(ec, recursiveFlag, trace)) \ OP (right->eval(ec, recursiveFlag, trace)) ); \ return val; \ } DECLARE_REL_EVAL(oLT,<) DECLARE_REL_EVAL(oLE,<=) DECLARE_REL_EVAL(oGT,>) DECLARE_REL_EVAL(oGE,>=)

问题 How can I simulate string + string expression via c# expression. The Expression.Add method does not work. string + string expression like "111" + "222" = "111222" thanks 回答1: You need to call into string.Concat (the C# compiler turns string concatenation into calls to string.Concat under the hood). var concatMethod = typeof(string).GetMethod("Concat", new[] { typeof(string), typeof(string) }); var first = Expression.Constant("a"); var second = Expression.Constant("b"); var concat = Expression

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 6 years ago . I'm not that good at Regex, Can you give me a pattern to match any php tags? [ <? , <?php ] if you have a nice and simple guide for Regex i'd be happy to have it too :) I already tried: '/^(<\?)$/' But it doesn't really help =/ Thanks! 回答1: You will need preg_match_all to match tags, plural. The below will match

问题 I have a plot and would like to add some regression statistics (e.g. F, R2, p) in the plot area. I am familiar with text() , but have been unable to find a comprehensive source of information with examples on how to build text strings with mathematical symbols, sub-and superscripts, etc. Any sources with detailed examples greatly appreciated. For example, I have a simple linear regression that I would like to extract the stats from and add them to my plot. For example reg1 <- lm(WW1 ~ PC1,

问题 Could anyone provide a clear (and easy to understand) explanation of what happens here (generally, generics, extension methods and Expression all together): public static MvcHtmlString TextBoxFor<TModel, TProperty> (this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression) { return htmlHelper.TextBoxFor(expression, format: null); } and further using of it here: Html.TextBoxFor(o => Model.SomeValue) The most problematic moment for the understanding is the way how

问题 I'm looking for a way to get the name and value of a proptery in a POCO object. I've tried many solutions but can't seem to get them to work. I really liked this older solution but it causes a null ref error. Here's kind of what I'm trying to do: public class POCO { public int ID { get; set; } public string Name { get; set; } public string Surname { get; set; } public string Description { get; set; } } public class POCOValidationResult { public bool IsValid { get; set; } public string Error {

问题 I need the below regex to select only those of total size X: [[JN]*P?[JN]*]N EDIT: e.g. for 6: JJPNNN -> JJPNNN ONNJNNNO -> NNJNNN NPJNJNN -> NPJNJN, PJNJNN NPJNN -> False I need it to capture the group. 回答1: You can use lookahead to first check the length, like this: (?=^.{6}$)[[JN]*P?[JN]*]N Also, you seem to have too many brackets. To make the expression match your examples, you need to remove the outermost one: (?=^.{6}$)[JN]*P?[JN]*N Here is a small demo using ideone. 回答2: You can use