ternary operator or if() statement for default value?

[lawpoop@gmail.com]

I'm trying to write some simple code, but I might be simplifying it
too much.

I have a function that either returns a string that I want, or FALSE.
In the code that I'm working on, I would like to default to another
string if the function returns false.

Here's the long way to do it:

$string = myFunction(2);
if ( $string === FALSE ) {
$string = "default value";

}

I would like to use the value from the function, if it's not false,
else the default value.

if ( $string = myFunction(2) === FALSE ) {
$string = "default value";

}

If I were using the ternary operator to do this, I would do

$string = myFunction(2) === FALSE ? "default value" : myFunction(2) ;

but it looks like I'm calling the function twice, which would be
inefficient.

What's the most efficient way to do this?

[Michael Fesser]

Re: ternary operator or if() statement for default value?

..oO(lawpoop@gm ail.com)

>I'm trying to write some simple code, but I might be simplifying it
>too much.
>
>I have a function that either returns a string that I want, or FALSE.
>In the code that I'm working on, I would like to default to another
>string if the function returns false.
>
>Here's the long way to do it:
>
>$string = myFunction(2);
>if ( $string === FALSE ) {
$string = "default value";
>
>}
>
>I would like to use the value from the function, if it's not false,
>else the default value.
>
>if ( $string = myFunction(2) === FALSE ) {
$string = "default value";
>
>}
>
>If I were using the ternary operator to do this, I would do
>
>$string = myFunction(2) === FALSE ? "default value" : myFunction(2) ;
>
>but it looks like I'm calling the function twice, which would be
>inefficient.
>
>What's the most efficient way to do this?

Efficiency is not really an issue. Question is what's more convenient
and what you feel more comfortable with. You could do something like

$string = ($value = myFunction(2)) === FALSE
? 'default value'
: $value;

But I would probably use a little helper function with two arguments:

function strInit($value, $default)
return ($value !== FALSE) ? $value : $default;
}

And then:

$string = strInit(myFunct ion(2), 'default value');

Micha

[lawpoop@gmail.com]

Re: ternary operator or if() statement for default value?

On Oct 9, 3:58 pm, Michael Fesser <neti...@gmx.de wrote:

Efficiency is not really an issue. Question is what's more convenient
and what you feel more comfortable with. You could do something like
>
$string = ($value = myFunction(2)) === FALSE
  ? 'default value'
  : $value;
>

Thanks, Micha! That's exactly what I was looking for!

[Michael Fesser]

Re: ternary operator or if() statement for default value?

..oO(lawpoop@gm ail.com)

>On Oct 9, 3:58 pm, Michael Fesser <neti...@gmx.de wrote:
>

>Efficiency is not really an issue. Question is what's more convenient
>and what you feel more comfortable with. You could do something like
>>
>$string = ($value = myFunction(2)) === FALSE
>  ? 'default value'
>  : $value;
>>

>
>Thanks, Micha! That's exactly what I was looking for!

You're welcome.

Micha

[Stewart Robert Hinsley]

Re: ternary operator or if() statement for default value?

In message
<9744b18b-8016-447b-9b81-a982f1a22edb@u4 6g2000hsc.googl egroups.com>,
lawpoop@gmail.c om writes

>I'm trying to write some simple code, but I might be simplifying it
>too much.
>
>I have a function that either returns a string that I want, or FALSE.
>In the code that I'm working on, I would like to default to another
>string if the function returns false.
>
>Here's the long way to do it:
>
>$string = myFunction(2);
>if ( $string === FALSE ) {
$string = "default value";
>
>}
>
>I would like to use the value from the function, if it's not false,
>else the default value.
>
>if ( $string = myFunction(2) === FALSE ) {
$string = "default value";
>
>}
>
>If I were using the ternary operator to do this, I would do
>
>$string = myFunction(2) === FALSE ? "default value" : myFunction(2) ;
>
>but it looks like I'm calling the function twice, which would be
>inefficient.

It's also problematic if the function has side effects.

>
>What's the most efficient way to do this?

Checking the manual, it appears that PHP has inherited C-like assignment
operator semantics, so

$string = ($temp = myFunction(2)) === FALSE ? "default value" : $temp;

--
Stewart Robert Hinsley

[lawpoop@gmail.com]

Re: ternary operator or if() statement for default value?

On Oct 9, 4:33 pm, Stewart Robert Hinsley <{$new...@meden .demon.co.uk>
wrote:

In message
<9744b18b-8016-447b-9b81-a982f1a22...@u4 6g2000hsc.googl egroups.com>,
lawp...@gmail.c om writes

>

If I were using the ternary operator to do this, I would do

>

$string = myFunction(2) === FALSE ? "default value" : myFunction(2) ;

>

but it looks like I'm calling the function twice, which would be
inefficient.

>
It's also problematic if the function has side effects.

"Side effects" being if the function returns anything other than a
valid string or false?

[Stewart Robert Hinsley]

Re: ternary operator or if() statement for default value?

In message
<b03b781b-c5da-4a94-9ffb-5633b2dc21fd@l3 3g2000pri.googl egroups.com>,
lawpoop@gmail.c om writes

>On Oct 9, 4:33 pm, Stewart Robert Hinsley <{$new...@meden .demon.co.uk>
>wrote:

>In message
><9744b18b-8016-447b-9b81-a982f1a22...@u4 6g2000hsc.googl egroups.com>,
>lawp...@gmail. com writes

>

>>

>If I were using the ternary operator to do this, I would do

>>

>$string = myFunction(2) === FALSE ? "default value" : myFunction(2) ;

>>

>but it looks like I'm calling the function twice, which would be
>inefficient.

>>
>It's also problematic if the function has side effects.

>
>"Side effects" being if the function returns anything other than a
>valid string or false?
>

Side effects being if the function changes any non-local or static
variable during its execution.

So it the function has internal state, and this changes when it is
called, that's a side effect. (For example a random number generator
function.)

So if the function changes any global variable (or class variables, if
it's a member function of a class) that's a side effect.

So if a function changes a variable passed to it as a reference, that's
a side effect.

Pascal distinguishes between procedures (which can have side effects)
and functions (which can't), but most languages only have a single
construct, which covers both concepts. (Some languages call them
functions, some procedures, some subroutines, and I wouldn't be
surprised if there were other alternate names.)
--
Stewart Robert Hinsley

[Michael Fesser]

Re: ternary operator or if() statement for default value?

..oO(Stewart Robert Hinsley)

>Side effects being if the function changes any non-local or static
>variable during its execution.
>
>So it the function has internal state, and this changes when it is
>called, that's a side effect. (For example a random number generator
>function.)
>
>So if the function changes any global variable (or class variables, if
>it's a member function of a class) that's a side effect.
>
>So if a function changes a variable passed to it as a reference, that's
>a side effect.
>
>Pascal distinguishes between procedures (which can have side effects)
>and functions (which can't),

Functions in Pascal can have side effects as well. The only difference
is that they have a return value, while procedures have not.

Micha

[Jerry Stuckle]

Re: ternary operator or if() statement for default value?

Stewart Robert Hinsley wrote:

In message
<b03b781b-c5da-4a94-9ffb-5633b2dc21fd@l3 3g2000pri.googl egroups.com>,
lawpoop@gmail.c om writes

>On Oct 9, 4:33 pm, Stewart Robert Hinsley <{$new...@meden .demon.co.uk>
>wrote:

>>In message
>><9744b18b-8016-447b-9b81-a982f1a22...@u4 6g2000hsc.googl egroups.com>,
>>lawp...@gmail .com writes

>>

>>>
>>If I were using the ternary operator to do this, I would do
>>>
>>$string = myFunction(2) === FALSE ? "default value" : myFunction(2) ;
>>>
>>but it looks like I'm calling the function twice, which would be
>>inefficient .
>>>
>>It's also problematic if the function has side effects.

>>
>"Side effects" being if the function returns anything other than a
>valid string or false?
>>

>
Side effects being if the function changes any non-local or static
variable during its execution.
>
So it the function has internal state, and this changes when it is
called, that's a side effect. (For example a random number generator
function.)
>
So if the function changes any global variable (or class variables, if
it's a member function of a class) that's a side effect.
>
So if a function changes a variable passed to it as a reference, that's
a side effect.
>
Pascal distinguishes between procedures (which can have side effects)
and functions (which can't), but most languages only have a single
construct, which covers both concepts. (Some languages call them
functions, some procedures, some subroutines, and I wouldn't be
surprised if there were other alternate names.)

Not quite true. In Pascal, a procedure cannot return a value, while a
function must return a value.

Either one can have side effects.

As for "most languages only have a single construct" - true of many
languages which are based at least in part on C. Other languages such
as FORTRAN, PL/1 and others have both concepts. In those which don't
distinguish between the two, the presence of a return value is optional.

--
=============== ===
Remove the "x" from my email address
Jerry Stuckle
JDS Computer Training Corp.
jstucklex@attgl obal.net
=============== ===

[Stewart Robert Hinsley]

Re: ternary operator or if() statement for default value?

In message <gco9br$e9o$1@r egistered.motza rella.org>, Jerry Stuckle
<jstucklex@attg lobal.netwrites

>Stewart Robert Hinsley wrote:

>In message
>><b03b781b-c5da-4a94-9ffb-5633b2dc21fd@l3 3g2000pri.googl egroups.com>,
>>lawpoop@gmail .com writes

>>On Oct 9, 4:33 pm, Stewart Robert Hinsley <{$new...@meden .demon.co.uk>
>>wrote:
>>>In message
>>><9744b18b-8016-447b-9b81-a982f1a22...@u4 6g2000hsc.googl egroups.com>,
>>>lawp...@gmai l.com writes
>>>
>>>>
>>>If I were using the ternary operator to do this, I would do
>>>>
>>>$string = myFunction(2) === FALSE ? "default value" : myFunction(2) ;
>>>>
>>>but it looks like I'm calling the function twice, which would be
>>>inefficien t.
>>>>
>>>It's also problematic if the function has side effects.
>>>
>>"Side effects" being if the function returns anything other than a
>>valid string or false?
>>>

> Side effects being if the function changes any non-local or static
>>variable during its execution.
> So it the function has internal state, and this changes when it is
>>called, that's a side effect. (For example a random number generator
>>function.)
> So if the function changes any global variable (or class variables,
>>if it's a member function of a class) that's a side effect.
> So if a function changes a variable passed to it as a reference,
>>that's a side effect.
> Pascal distinguishes between procedures (which can have side
>>effects) and functions (which can't), but most languages only have a
>>single construct, which covers both concepts. (Some languages call
>>them functions, some procedures, some subroutines, and I wouldn't be
>>surprised if there were other alternate names.)

>
>Not quite true. In Pascal, a procedure cannot return a value, while a
>function must return a value.

Yes - I shouldn't have relied on my memory from the 25 years or more
since I used Pascal. Jensen and Wirth wrote "strongly discouraged".

>
>Either one can have side effects.
>
>As for "most languages only have a single construct" - true of many
>languages which are based at least in part on C. Other languages such
>as FORTRAN, PL/1 and others have both concepts. In those which don't
>distinguish between the two, the presence of a return value is optional.
>

--
Stewart Robert Hinsley