Hi Monty,
On 04/20/2017 09:35 AM, Michael Widenius wrote: > Hi! > > On 20 Apr 2017 06:10, "Alexander Barkov" <[email protected] > <mailto:[email protected]>> wrote: > > Hello all, > > > Monty is now doing refactoring: > > 1. Replacing a lot of LEX_STRING to LEX_CSTRING. > > 2. Fixing functions and methods that have arguments of types: > a. pointer "const LEX_STRING *name" and > b. reference "const LEX_STRING &name". > to the same style. Monty chose passing by pointer (2a). > > > I think that: > > - #1 is good. > - #2 is good, in the sense of changing to the same style. > > But I think that the choice of "passing by pointer" in #2 is bad. > Passing by reference for LEX_STRING/LEX_CSTRING related things would be > better. > > > With the "passing by pointer" approach whenever one needs to pass > a LEX_STRING to a function accepting LEX_CSTRING, one will have to do: > > > void func1(const LEX_STRING *str) > { > LEX_CSTRING tmp= {str->str, str->length}; > func2(&tmp); > } > > The above is not a problem: > > > - We don't have less than 5 places in the code where LEX_STRING is > changed to LEX_CSTRING. > - In these places one can do this with a simple cast, nothing elaborated. There are more examples: Item_str_func(THD *thd): Item_func(thd) { decimals=NOT_FIXED_DEC; } Item_str_func(THD *thd, Item *a): Item_func(thd, a) {decimals=NOT_FIXED_DEC; } Item_str_func(THD *thd, Item *a, Item *b): Item_func(thd, a, b) { decimals=NOT_FIXED_DEC; } Item_str_func(THD *thd, Item *a, Item *b, Item *c): Item_func(thd, a, b, c) { decimals=NOT_FIXED_DEC; } Item_str_func(THD *thd, Item *a, Item *b, Item *c, Item *d): Item_func(thd, a, b, c, d) { decimals=NOT_FIXED_DEC; } Item_str_func(THD *thd, Item *a, Item *b, Item *c, Item *d, Item* e): Item_func(thd, a, b, c, d, e) { decimals=NOT_FIXED_DEC; } Item_str_func(THD *thd, List<Item> &list): Item_func(thd, list) { decimals=NOT_FIXED_DEC; } This is terrible. The same thing in Item_int_func, Item_real_func, Item_decimal_func, etc, etc. There is only one constructor needed for all of them. For example, for Item_str_func: Item_str_func(THD *thd, const Item_args &args): Item_func(thd, args) { decimals=NOT_FIXED_DEC; } And when you need to call new, you do: Item *item= new (thd->mem_root) Item_func_somefunc(thd, Item_args(a,b,c)); You cannot do this with the "pass by pointer" approach. > > > > I'd propose two things instead: > > 1. Add a class: > > > No reason to make a complex solution for a problem that doesn't exist. It's a trivial solution. The problem does exists. The current code absolutely is excessive and inconvenient to use. > > 2. Instead of "const LEX_CSTRING *str" > we use "const Lex_cstring &str" all around C++ code. > > > No, no, no. > > I do not want to use & anywhere as arguments in the code. It hides > things and lends people to do errors like we had before where they > declared some functions to take full structure she references in other > places, which creates a mess. I don't propose to use pass-by-value: func(Some_class arg); I propose to use pass-by-reference: func(const Some_class &) When you do: func(some_class_instance); pass-by-value requires a constructor call, indeed. but pass-by-reference does not need a constructor call! pass-by-reference compiles to exactly the same thing with pass-by-pointer: it puts the address of the object to the stack. Nothing else. > > Regards, > Monty _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
