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Remove deriving(ToStr) #12412

Merged
merged 2 commits into from
Feb 24, 2014
Merged

Remove deriving(ToStr) #12412

merged 2 commits into from
Feb 24, 2014

Commits on Feb 24, 2014

  1. Remove all ToStr impls, add Show impls 

    This commit changes the ToStr trait to:

    impl<T: fmt::Show> ToStr for T {
        fn to_str(&self) -> ~str { format!("{}", *self) }
    }

The ToStr trait has been on the chopping block for quite awhile now, and this is
the final nail in its coffin. The trait and the corresponding method are not
being removed as part of this commit, but rather any implementations of the
`ToStr` trait are being forbidden because of the generic impl. The new way to
get the `to_str()` method to work is to implement `fmt::Show`.

Formatting into a `&mut Writer` (as `format!` does) is much more efficient than
`ToStr` when building up large strings. The `ToStr` trait forces many
intermediate allocations to be made while the `fmt::Show` trait allows
incremental buildup in the same heap allocated buffer. Additionally, the
`fmt::Show` trait is much more extensible in terms of interoperation with other
`Writer` instances and in more situations. By design the `ToStr` trait requires
at least one allocation whereas the `fmt::Show` trait does not require any
allocations.

Closes rust-lang#8242
Closes rust-lang#9806
    @alexcrichton
    alexcrichton committed Feb 24, 2014
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  2. Remove deriving(ToStr) 

    This has been superseded by deriving(Show).

cc rust-lang#9806
    @alexcrichton
    alexcrichton committed Feb 24, 2014
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