What's the point of DSLs / fluent interfaces

Question

I was recently watching a webcast about how to create a fluent DSL and I have to admit, I don\'t understand the reasons why one would use such an approach (at least for the give

Answer 1

Consider:

sizer.ResizeImage(inputImage, outputImage, 0.5, ImageFormat.Jpeg);

What if you used less clear variable names:

sizer.ResizeImage(i, o, x, ImageFormat.Jpeg);

Imagine you've printed this code out. It's harder to infer what these arguments are, as you don't have access to the method signature.

With the fluent interface, this is clearer:

 sizer.FromImage(i)
 .ToLocation(o)
 .ReduceByPercent(x)
 .OutputImageFormat(ImageFormat.Jpeg)
 .Save();

Also, the order of methods is not important. This is equivalent:

 sizer.FromImage(i)
 .ReduceByPercent(x)
 .OutputImageFormat(ImageFormat.Jpeg)
 .ToLocation(o)
 .Save();

In addition, perhaps you might have defaults for the output image format, and the reduction, so this could become:

 sizer.FromImage(i)
 .ToLocation(o)
 .Save();

This would require overloaded constructors to achieve the same effect.