boolean-logic

问题 I am using && like this and it works typeof foo === 'function' && foo(); //if foo exist then call it instead of if (typeof foo === 'function') { foo(); } Is it wrong to do or just a matter of style and taste? For me it is natural and I want to use && , but now a linter complained: Expected an assignment or function call and instead saw an expression. Can there be any real issues here or is it just a matter of convention? Here is a code snippet: function foo(x) { console.log("foo say " + x) }

问题 I am using && like this and it works typeof foo === 'function' && foo(); //if foo exist then call it instead of if (typeof foo === 'function') { foo(); } Is it wrong to do or just a matter of style and taste? For me it is natural and I want to use && , but now a linter complained: Expected an assignment or function call and instead saw an expression. Can there be any real issues here or is it just a matter of convention? Here is a code snippet: function foo(x) { console.log("foo say " + x) }

来源： https://stackoverflow.com/questions/64394487/if-either-can-be-either-left-or-right-but-not-both-then-why-does-it-correspond

问题 How can I check if 20 variables are all true, or if 20 variables are all false? if possible without using a really long if ... the variables are actually array elements: array('a'=> true, 'b'=> true ...) to make it more clear: if the array has both true and false values return nothing if the array has only true values return true if the array has only false values return false :) 回答1: if(count(array_unique($your_array)) === 1) return current($your_array); else return; 回答2: You could use in

问题 I am trying to write a query to pull data from my Neo4J database. Lets say there are five conditions that determine whether or not I want to pull _____ from my database: A, B, C, D, and E. The boolean expression which determines this is: A && B && (C || D || E) From scouring the web, I cannot find any information about an order of operations that Neo4J AND and OR queries abide by (AND usually precedes OR), but from my observations they seem like they execute sequentially. Since there is no

问题 I'm trying to make a function that will compare multiple variables to an integer and output a string of three letters. I was wondering if there was a way to translate this into Python. So say: x = 0 y = 1 z = 3 mylist = [] if x or y or z == 0 : mylist.append("c") if x or y or z == 1 : mylist.append("d") if x or y or z == 2 : mylist.append("e") if x or y or z == 3 : mylist.append("f") which would return a list of ["c", "d", "f"] Is something like this possible? 回答1: You misunderstand how

问题 I have a Window with two tabs, that holds two different user controls. In order to enable/disable navigation to the second tab, I implement an IsEnabled property in both VM's from the IPageViewModel interface. The IsEnabled boolean property is set to true when a SelectedCustomer is received in the CustomerOrdersViewModel , via Messenger service from CustomerDetailsViewModel . So far this method works, as the second tab is enabled when I select a customer from the data grid in the first view.

问题 I have a 2-1 mux and I'm trying to write z = s'd0 + sd1 using only NAND , XNOR , and OR gates (not necessarily all of them). I tried simplifying it and what I ended up with is z = NAND(NAND(s', d0), NAND(s, d1)) , but I can't use NOT ( ' ), so is there a way to write NAND(s', d0) without the NOT ? 回答1: You can build NOT from NAND: NAND(X,X) == NOT(X) 回答2: NAND gate is an universal gate; you can use it to make any other gate. s' = nand(s,s) 回答3: Initial solution Full version of the solution

问题 I have the powershell code $target_dir = "\\server\share\" $DelTmpStatus = "init value" if ( Test-Path ( $target_dir + "receivals.tmp") ) { del ( $target_dir + "receivals.tmp") $DelTmpStatus = "Present and delete status $?" } else { $DelTmpStatus = "NA" } and sometimes it makes it through this section with $DelTmpStatus still set to "init value". How can the if-else structure not follow either path? Does the if-else structure in powershell not do anything when the if function is given an

问题 Take the following expression: FALSE AND (expression) Will MySQL evaluate the expression or just move on as soon as it sees FALSE ? Some background context-- I wanted to speed up a query by doing: JOIN... ON (indexed_column1=indexed_column2 AND non_indexed_column_a=non_indexed_column_b) For background on why I'm doing this query see this answer If it's going to always evaluate non_indexed_column_a=non_indexed_column_b then no time is saved with that. 回答1: The MySQL query optimizer uses