Why does the documentation use "iff" instead of "if"?
iff is used for if and only if statement.
Statement enclosed is going to executed if both condition must be true.
ie. either both are true or none.
Related
I am having a hard time having jemeter working with my if condition
As you see the above I am checking is status variable which I created in earlier car is true and it is true so I expect this if gets executed but it does not. However as soon as I change it to
It works fine.
I need these kind of check for sure(for a case like ${status} == false)
Am I missing anything?
** Update **
when I disable interpret regx I can see it works
This is expected behaviour.
In If Controller When you uncheck "Interpret condition as Variable Expression", Javascript is used to evaluate :
${status} == true
So it works, but it hurts badly performances.
So instead and as per reference documentation:
Option 2 : Use a function (${__jexl3()} is advised) to evaluate an expression that must return true or false
So keep "Interpret condition as Variable Expression" checked and use __jexl3 function:
${__jexl3(${status} == true,)}
This give you:
The conditional construct of if command looks like this:
if TEST-COMMANDS; then
CONSEQUENT-COMMANDS;
[elif MORE-TEST-COMMANDS; then
MORE-CONSEQUENTS;]
[else ALTERNATE-CONSEQUENTS;]
fi
And the loop construct of while command looks like this:
while TEST-COMMANDS; do CONSEQUENT-COMMANDS; done
I was wondering why then is needed in if command but not in while command? Why couldn't it be ommited?
do in the while syntax serves a similar purpose to then in the if syntax. They both signify the start of the body of the statement - differentiating it from the condition part of the statement.
The if conditional statement is a compound statement in the shell. The if & then sections of the statement are executed as two parts, the then section is only invoked if the if section ends with an exit status of 0. Both sections may contain multiple statements; therefore, a semi-colon alone is insufficient to separate these sections.
Like #shibley is saying in his answer, the do and then words are used to indicate the beginning of the block of actions to perform.
I have done some research and could not find the historical reasons, so I am going to guess the logical ones. It might be too subjective, so do not hesitate to comment your impressions below.
The bash syntax is quite "symmetrical": Whenever you have an case you finish it with esac. Also, it was designed in a very human way, so it is easily understandable.
That said, if you are in a while loop, it means that you are going to do something while a condition is true. Then, when it is not true anymore you are done.
However, in an if condition, you are saying that if something happens, then something needs to be executed.
In short: do and then are human-readable ways to indicate the same, that is, the beginning of a block of commands to be performed upon a while or if condition.
So I have a keyword driven framework that executes on keywords. In one of the functions I have a if element exist condition. Now if that element doesn't exist I want qtp to not execute the next 3 keyword functions following it. Is there a way to do this? Thank you!
You could a global variable that records the number of keywords that should be skipped. When your element doesn't exist, you could set the skip count to 3. In your framework that reads each keyword, you could first check the current skip count. If it's 0, you execute the keyword normally. Otherwise, you decrease the skip count by 1 and exit without executing that keyword.
Can you not insert a conditional statement?
Therefore if the element exists, you can put the next 3 statements within the loop? Else, do nothing. Then have the code follow on as normal?
If you aren't comfortable in expert view, this shows how to do it in keyword view also:
http://www.softwaretestinghelp.com/conditional-loop-statements-qtp-tutorial-4/
Is the keyword unless the same as if?
When do you use ??
I've seen:
if someobject?
I know it checks against nil correct?
Is the keyword 'unless' the same as 'if' ?
No, it's the opposite.
unless foo is the same as if !foo
if someobject?
I know it checks against nil correct?
No it calls a method named someobject?. I.e. the ? is just part of the method name.
? can be used in methodnames, but only as the last character. Conventionally it is used to name methods which return a boolean value (i.e. either true or false).
? can also be used as part of the conditional operator condition ? then_part : else_part, but that's not how it is used in your example.
unless is actually the opposite of if. unless condition is equivalent to if !condition.
Which one you use depends on what feels more natural to the intention you're expressing in code.
e.g.
unless file_exists?
# create file
end
vs.
if !file_exists?
# create file
end
Regarding ?, there is a convention for boolean methods in Ruby to end with a ?.
This statement:
unless conditional expression
Is the equivalent to:
if not (conditional expression)
In Ruby you can end your method names with a question mark which is normally used to show that it is a boolean method.
With Rails a check against nil would look like this:
someobject.nil?
This calls the nil?() method of the object, which returns true for NilObject and false for anything else.
I think the convention for ?-suffix is to use it when naming a method that returns a boolean value. It is not a special character, but is used to make the name of the method easier to understand, or at least I think that's what the intention was. It's to make it clear that the method is like asking a question: it shouldn't change anything, only return some kind of status...
There's also !-suffix that I think by convention means that the method may have side-effects or may modify the object it is called on (rather than return a modified copy). Either way, the ! is to make you think carefully about calling such a method and to make sure you understand what that method does.
I don't think anything enforces these conventions (I've never tried to break them) so of course you could abuse them horribly, but your fellow developers would not be happy working with your code.
for unless see here: http://railstips.org/blog/archives/2008/12/01/unless-the-abused-ruby-conditional/
if someobject?
The appending of a '?' here only means that it returns a boolean.
I was wondering, how would I use the underscore twice but check that both instances of that underscore unify?
What I basically need is something that returns true if two elements of the same value in one mapping exist...
I.E member((_,_),[(a,a),(b,a),(c,a)]).
If I use a variable does that make them unified?
I.E member((A,A),[(a,a),(b,a),(c,a)]).
But it returns the variable rather than true.
I need some enlightenment.
Your solution with a variable is correct.
Returning a variable is a way to return true. It really means: this goal is true when var = value, as opposed to this goal is true.
Note that using this as a clause in a different predicate will hide the variable:
contains_identical_pair(List) :- member((A,A),List).
You can use double negation to avoid variable bindings:
?- \+ \+ member((A,A),[(a,a),(b,a),(c,a)]).
true.
The bindings for the variables printed on the prolog screen are just there to make life easier in an interactive prompt so that you don't have to print out the variables you care about each time. They don't affect the logic of your code at all.
They will only be printed for variables are are entered at the prompt. So if the predicate you are writing is part of a larger program, you can just ignore this output, or if you want this to be a top-level predicate that people will call from the prompt and you don't want the output printed, then simply wrap your call in a predicate that has no arguments or has only input arguments. ie:
wrapper :-
predicate(Out1,Out2).
or:
wrapper(In1,In2) :-
predicate(In1,In2,Out1,Out2).