This context encapsulate all the datas needed to evaluate a SearchExpression and it allows user to interact with the evaluation runtime of an expression. A SearchExpressionContext is created automatically with a SearchExpressionRuntime anytime SearchExpression.Execute is called.
Here is an example showing ow the SearchExpressionContext is used during evaluation:
[SearchExpressionEvaluator(SearchExpressionType.Iterable | SearchExpressionType.Variadic)] [SearchExpressionEvaluatorSignatureOverload(SearchExpressionType.Number, SearchExpressionType.Iterable | SearchExpressionType.Variadic)] [Description("Extract and returns the X first results for each expression.")] public static IEnumerable<SearchItem> TakeXFirst(SearchExpressionContext c) { var argIndex = 0; var takeNumber = 1; if (c.args[0].types.HasFlag(SearchExpressionType.Number)) { ++argIndex; takeNumber = Math.Max((int)(c.args[0].GetNumberValue(takeNumber)), 0); } for ( ; argIndex < c.args.Length; ++argIndex) { var iterable = c.args[argIndex].Execute(c); var taken = 0; foreach (var item in iterable) { if (item == null) yield return null; else { yield return item; ++taken; if (taken == takeNumber) { c.Break(); break; } } } } }
| args | Arguments of passed to the SearchExpression being evaluated. |
| expression | [[]SearchExpression] being evaluated. |
| items | SearchItems yielded by the evaluation of a searchExpression. |
| runtime | SearchExpressionRuntime associated with this context. The runtime stores all runtime data (stack frames, stack of contex and items) necessary for evaluation of a SearchExpression. |
| search | SearchContex containing the search query that was parsed to create the SearchExpression. |
| valid | Is the current context valid or not. If invalid it means the associated SearchExpression is null or the SearchExiressionRuntime is invalid. |
| Break | Break the evaluation of a SearchExpression meaning items won't be yielded anymore. |
| Continue | Tell SearchExpression evaluation to continue. |
| IsBreaking | Has the current context being flagged to break execution? |
| IsContinuing | Has the current context being flagged to continue execution? |
| ResetIterationControl | Restart evaluation and iteration of SearchExpression. |
| ResolveAlias | Try to resolve an alias value using the SearchExpressionRuntime attached to this context. Each frame if asked to resolve a SearchExpression.alias. |
| ThrowError | Stop a SearchExpression evaluation by throwing a SearchExceptionEvaluatorException. User writing an evaluator can decide to throw thse exceptions if the parameters passed to evaluation are not valid or if a problem happens during evaluation. |
| ToString | Get string representation of a context. |