Merge condition check codes in compose() method

[QianJianhua1]

Summary

Merge condition check codes in compose() method.

Details and comments

Merge the two consecutive "if front" check codes into one.

[kdk]

Thanks @QianJianhua1 , I agree these two if statements could be merged (though I would expect the performance improvement in doing so to be small). However, to me, I find the updated version less readable than the original (having this as two conditions did separate out the "merge _data lists" phase from the "update ParameterTable" phase, and the comment # just append new parameters is now misplaced). Is there a way the readability of the original could be preserved?

[QianJianhua1]

Thank you @kdk Partly agree with you. But if you think of "update _data" and "update parameter" as one continuous process, you might think otherwise. In other words, after _data is updated, parameter must be updated.
if front is true, we just consider how to deal with them(contain _data and parameter), Otherwise just append the new part.
I have changed the comments, please review it again.

[javabster]

This lgtm, thanks @QianJianhua1!

[jakelishman]

On this one I agree with @QianJianhua1 about the newer readability: in the previous version with its split if statements, it wasn't super clear why you needed to invalidate the parameter table in the second if front, unless you also saw the first if front. Putting them together, it's very clear to me - we have to invalidate it because data has been inserted before, so all previous indices are now invalid.

[kdk]

Thanks for the updates @QianJianhua1 , this LGTM!