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Implied Print: New Command Line Feature in IDL 8.3

Jim Pendleton
As is the case with our customers, those at Exelis use the right tools for the job. When IDL and its Workbench don't yet have some functionality that would make our development efforts most efficient and cost-effective, we'll use a different tool. Not often, but it happens.

Our Professional Services Group, in particular, thrives in mixed-mode environments like this. 

Sometimes we and our customers encounter productivity features in other environments that lead us to ask ourselves, "Wouldn't it be cool if IDL could do this, too?" And sometimes, if the business case can be made for it, the question isn't rhetorical and the reply is a resounding "Yes!"

The "implied print" behavior at the IDL command line is just such a feature that's new to version 8.3.  It incorporates and expands upon some good ideas we've seen. It has been a frequently-requested item from our customers, as well.

Like atmospheric oxygen, once you start using it, you'll wonder how you ever functioned without it. No kidding.

Remember this old saw?

IDL> PRINT, 2 + 2

       4

Well, forget everything you've learned about using PRINT.  Behold implied print:

IDL> 2+2

       4

Not to exaggerate at all, but it's like a lightning bolt overloading all your neurons right now, isn't it? Think of all the years of accumulated effort you've expended typing "PRINT," or worse yet "PRITN" or forgetting the required comma. No more.

Again, not to overstate this at all, but the tyranny of PRINT has been relegated to the dustbin of history.

Here are other examples:

IDL> a = BINDGEN(5)

IDL> a

  0   1   2  3   4

IDL> a[2:4]

  2   3   4

IDL> SIN(a)

      0.00000000      0.84147096      0.90929741      0.14112000     -0.75680250

But wait, there's more! Implied print will automatically display the maximum number of digits of precision for floating-point and double-precision data. Here are some comparisons between the default PRINT behavior (which will not change, to support backward compatibility) and the new implied print behavior:

IDL> print, 1.2345678

      1.23457

IDL> 1.2345678

       1.2345678

IDL> print, !dpi

       3.1415927

IDL> !dpi

      3.1415926535897931

There are new behaviors for string arrays, LISTs, HASHes, and structures, too.

If you write object-oriented code using the IDL_Object superclass, overriding the new _overloadImpliedPrint method will allow you to automatically extend this functionality to your own classes, similar to _overloadPrint . You may choose to have one simply call the other, or differentiate their behaviors. It keeps getting better and better, doesn't it?

This is all well and good at the command line, but what if you prefer this new style of output within an executing application or utility? The FIX, PRINT, and STRING functions all now accept a new IMPLIED_PRINT keyword that will use the same rules for output as implied print.

Yes, it's a revolution and you may have your cake and eat it, too.

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