Is there a way to do ternary operators in Velocity?
This is what I'd like to do:
#set ($name = ($args.get(0) == "") ? "default" : $args.get(0))
Instead of chunky if-else
#if ($args.get(0) == "")
#set ($name = "default")
#else
#set ($name = $args.get(0))
#end
Any ideas?
From experience and reading the VTL Reference there is no way to do this. If you had lots of assignments like this maybe you could look at defining your own velocimacro to try and avoid repeating the if else.
For example, if the macro only prints a single string you could do the following:
#set ($name = "#condOpt($args.get(0), "default")")
The double quotes around the macro call are important as that means the RHS of the #set is parsed.
I ended up doing as you said, Mark:
#macro(condOp $check, $default)
#if ($check == "")
$default
#else
$check
#end
#end
And then I can call it like so:
#set ($name = "#condOp($args.get(0), 'default')")
For the record, with Velocity 2.1+, you can provide alternate reference values:
${args[0]|'default'}
Related
I want to write the following if - else logic in Velocity
If $var1 == NONE
( If $subvar1 != 'null'
return True
else
return Failed_Sub1)
Else
If $subvar2 != 'null'
return True
else
return Failed_Sub2
So basically $subvar2 is only evaluated if $var != NONE and $subvar1 is only evaluated if $var == NONE
I tried something like
#if($var1 != 'NONE')
#if($subvar2 != 'null')True
#{else}Failed_Sub2
#end
#else
#if($subvar1 != 'null')True
#{else}Failed_Sub1
#end
#end
But its returning nothing to me. What am I doing wrong?
Do you want to avoid null values or strings containing 'null'?
In velocity, you can check for nulls using any non assigned reference, for instance $null :
#if($var1 == $null)
...
Otherwise than that, your code looks fine and nested #if statements are definitely possible.
Here's the relevant documentation.
I want to know what is the equivalent of this if statement:
if (condition) {
// do something
}else{
// do nothing
}
Using the conditional operator:
(condition) ? // [do nothing] : {do nothing} "
It's not possible to "do nothing" using the conditional operator. You always have to have valid expressions on both sides, although both expressions can be casted to void.
This is one of the dis-advantage of ternary operator ( ?: ).
It needs expressions in all the three places. You cant skip any of them.
You can do some tweak on it, however its True-part and / or False-part can be assigned to the same as :
int big=100;
big= (10 > 100) ? 0 : big;
if (!condition) {
// do something
}else{
// do nothing
}
Take a look at the !before contition now :-)
The ! before the condition just switches the "if", to "if not"...
Is that what you have been searching for?
originalValue = (condition) ? newValue : originalValue
The compiler should then remove the unnecessary assign of originalValue to itself.
GCC had an extension to do give you something more to what you where looking for, something like
originalValue = condition ?: newValue;
So it may be available in clang also. You would have to ! the condition though.
you could do something like this
someBool ? [self someFunction] : (^{})(); //empty block
In normal code the answer is there is no equivalent - all sub expressions of an expression must have a value, but...
the following is not a recommendation
Something along the lines of the following should work in the general case:
condition ? ( (^{ do something })(), 0 ) : 0;
That is for the general case. If do something is a single, non-compound, statement; such as a method call; then the block can be dropped to give:
condition ? (do something, 0) : 0;
Again this is NOT recommended in real code!
I'd like to use
#define IS_APP_FULL_VERSION NO
and the code
isAppFullVersion = IS_APP_FULL_VERSION;
to set instance variable. But is there a way to also do
#if IS_APP_FULL_VERSION == "NO"
// add some methods here
#endif
but it would give a compile error, and so is #if (IS_APP_FULL_VERSION == "NO"). Is there a way to check it against YES and NO? (check against the substitution value)
Update: it seems like > and == 0 is allowed, such as
#if IS_APP_FULL_VERSION == 0
so we can actually use 0 and 1 for false and true, and use == 1 to test, but it will be better if YES and NO can be used.
Update 2:
One possible solution turns out to be:
#define IS_APP_FULL_VERSION 1
#if IS_APP_FULL_VERSION
// add some methods here
#endif
isAppFullVersion = IS_APP_FULL_VERSION;
will all work, and we can just change 1 to 0 to toggle the code.
Your basic problem is that the macro processor #if statement only has one data type -- integer. All #if expressions are evaluated in integer, with undefined symbols being replaced with zero. String expressions (including comparisons) cannot be evaluated.
Actually, normally, I would just use a flag macro rather than a value one, since there's only two cases here:
#define APP_IS_FULL_VERSION
Either define or don't define that macro. Then, if you later wanted to include/exclude code based on that, you can use:
#ifdef APP_IS_FULL_VERSION
// Do something
#endif
(or #ifndef for the opposite case, obviously).
For the code segment, it's a simple matter of using that to select the correct code:
#ifdef APP_IS_FULL_VERSION
isAppFullVersion = YES;
#else
isAppFullVersion = NO;
#endif
I think, you're some confused comparison MACRO.
#define format is following it.
#define MACRO_NAME VALUE (VALUE is blank spaces are also fine. MACRO_NAME need is.)
if you want comparison compile-time following like it. this is comparison mean only defined vs no defined. not YES vs NO
#define IS_APP_FULL_VERSION 1
#if defined IS_APP_FULL_VERSION
NSLog(#"full-verison");
#endif
#define IS_APP_FULL_VERSION blahblah
#if defined IS_APP_FULL_VERSION
NSLog(#"full-verison");
#endif
If you want to build separate versions of. refer a following like it.
#define IS_APP_FREE_VERSION
#if defined IS_APP_FREE_VERSION
NSLog(#"free-version");
#endif
#define IS_APP_FULL_VERSION
#if defined IS_APP_FULL_VERISON
NSLog(#"full-version");
#endif
if you want comparison runtime following like it. this is comparsion normally.
#define IS_APP_FULL_VERSION 1
if(IS_APP_FULL_VERSION)
{
NSLog(#"full-verison");
}
#define IS_APP_FULL_VERSION 0
if(!IS_APP_FULL_VERSION)
{
NSLog(#"no full-version");
}
I have this velocity template. It works fine in one case, but doesn't in another. If I remove the elseif it works fine. Has anyone encountered this?
#if (some condition)
## Do something
#elseif
## Do something else
#end
I don't know Velocity, but normally elseif is used with a second condition.
else seems to be what you need.
#if (some condition)
## Do something
#else
## Do something else
#end
If you are using #elseif statement then you should make sure that you are checking some condition inside that #elseif statement.
Eg :-
#if (some condition)
## Do something
#elseif (some condition)
## Do something
#else
## Do something else
#end
You can refer to this:
Apache Velocity User Guide
Basically it has to go according to one of the cases below:
#if ( condition )
##do something
#end
#if ( condition )
##do something
#else
##do something
#end
#if ( condition )
##do something
#elseif ( condition )
##do something
#else
##do something
#end
(The if-elseif-....-else ladder length can be long)
I'm looking at some open source projects and I'm seeing the following:
NSLog(#"%s w=%f, h=%f", #size, size.width, size.height)
What exactly is the meaning of '#' right before the size symbol? Is that some kind of prefix for C strings?
To elaborate on dirkgently's answer, this looks like the implementation of a macro that takes an NSSize (or similar) argument, and prints the name of the variable (which is what the # is doing; converting the name of the variable to a string containing the name of the variable) and then its values. So in:
NSSize fooSize = NSMakeSize(2, 3);
MACRO_NAME_HERE(fooSize);
the macro would expand to:
NSLog(#"%s w=%f h=%f", "fooSize", fooSize.width, fooSize.height);
and print:
fooSize w=2.0 h=3.0
(similar to NSStringFromSize, but with the variable name)
The official name of # is the stringizing operator. It takes its argument and surrounds it in quotes to make a C string constant, escaping any embedded quotes or backslashes as necessary. It is only allowed inside the definition of a macro -- it is not allowed in regular code. For example:
// This is not legal C
const char *str = #test
// This is ok
#define STRINGIZE(x) #x
const char *str1 = STRINGIZE(test); // equivalent to str1 = "test";
const char *str2 = STRINGIZE(test2"a\""); // equivalent to str2 = "test2\"a\\\"";
A related preprocessor operator is the token-pasting operator ##. It takes two tokens and pastes them together to get one token. Like the stringizing operator, it is only allowed in macro definitions, not in regular code.
// This is not legal C
int foobar = 3;
int x = foo ## bar;
// This is ok
#define TOKENPASTE(x, y) x ## y
int foobar = 3;
int x = TOKENPASTE(foo, bar); // equivalent to x = foobar;
Is this the body of a macro definition? Then the # could be used to stringize the following identifier i.e. to print "string" (without the codes).