when refering to type-pool you need to use TYPE 
declaration, and LIKE is used to refer your already 
declared variable. And for declaring native types 'N' 'C' 
you cannot use LIKE there.

data: matnr like mara-matnr,
      matnr1 type mara-matnr. 

will not make any difference in the program. however

data: matnr type mara-matnr,
      matnr1 like matnr. when the attribute of matnr 
changes will affect matnr1 also. 

and LIKE statement become obselete in Object programming. 
you can use TYPE statements only there.