operator-precedence

来源： https://stackoverflow.com/questions/49895131/logical-vs-assignment-operator-precedence-in-php

来源： https://stackoverflow.com/questions/63213860/why-does-the-javafx-css-order-of-precedence-differ-between-text-and-controls

问题 Why does (1 == 2 != 3) evaluate to False in Python, while both ((1 == 2) != 3) and (1 == (2 != 3)) evaluate to True ? What operator precedence is used here? 回答1: This is due to the operators chaining phenomenon. The Pydoc explains it as : Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z , except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false). And if you look at the precedence of the == and !

问题 Why does (1 == 2 != 3) evaluate to False in Python, while both ((1 == 2) != 3) and (1 == (2 != 3)) evaluate to True ? What operator precedence is used here? 回答1: This is due to the operators chaining phenomenon. The Pydoc explains it as : Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z , except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false). And if you look at the precedence of the == and !

问题 We are currently in the /home/student/ directory. We execute the following commands: pwd; (ls) || { cd .. && ls student/; } && cd student || cd / && cd ; The commands that are executed are: pwd, ls, cd student, cd /, cd Here is what I think: pwd is executed, because it's the first command (ls) is executed in a subshell, because the commands are seperated with ";" the code on the right of || isn't executed, since the code on the left of || was executed So far everything clear, I guess. But I

问题 We are currently in the /home/student/ directory. We execute the following commands: pwd; (ls) || { cd .. && ls student/; } && cd student || cd / && cd ; The commands that are executed are: pwd, ls, cd student, cd /, cd Here is what I think: pwd is executed, because it's the first command (ls) is executed in a subshell, because the commands are seperated with ";" the code on the right of || isn't executed, since the code on the left of || was executed So far everything clear, I guess. But I

问题 An issue of streams, internal string, and operation ordering with MSVC versus GCC / Clang Hello everyone, I just recently began to work more seriously with MSVC for a cross-platform project of mine, and while testing outputs via chained STD stream ( ie. a succession of obj.foo() << endl << obj.bar() << endl << [..etc] ) I came across a behavior when using internally updated string neither did I expected nor had encountered on Linux with GCC or Clang . Compiler versions were GCC 7.5, Clang 11

问题 An issue of streams, internal string, and operation ordering with MSVC versus GCC / Clang Hello everyone, I just recently began to work more seriously with MSVC for a cross-platform project of mine, and while testing outputs via chained STD stream ( ie. a succession of obj.foo() << endl << obj.bar() << endl << [..etc] ) I came across a behavior when using internally updated string neither did I expected nor had encountered on Linux with GCC or Clang . Compiler versions were GCC 7.5, Clang 11

问题 Is there any possible way to achieve a non-lazy left to right invocation of operations on a list in python ? e.g. scala val a = ((1 to 50) .map(_ * 4) .filter( _ <= 170) .filter(_.toString.length == 2) .filter (_ % 20 == 0) .zipWithIndex .map{ case(x,n) => s"Result[$n]=$x"} .mkString(" .. ")) a: String = Result[0]=20 .. Result[1]=40 .. Result[2]=60 .. Result[3]=80 While I realize many folks will not prefer the above syntax, I like the ability to move left to right and add arbitrary operations

问题 What is the default operator precedence in Oracle's regular expressions when they don't contain parentheses? For example, given H|ha+ would it be evaluated as H|h and then concatenated to a as in ((H|h)a) , or would the H be alternated with ha as in (H|(ha)) ? Also, when does the + kick in, etc.? 回答1: Given the Oracle doc: Table 4-2 lists the list of metacharacters supported for use in regular expressions passed to SQL regular expression functions and conditions. These metacharacters conform