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src/test/run-pass/default-ty-param-fallback
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+ // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
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+ // file at the top-level directory of this distribution and at
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+ // http://rust-lang.org/COPYRIGHT.
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+ //
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+ // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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+ // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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+ // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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+ // option. This file may not be copied, modified, or distributed
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+ // except according to those terms.
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+
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+ #![ feature( default_type_parameter_fallback) ]
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+ #![ feature( specialization) ]
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+
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+ use std:: fmt:: Debug ;
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+
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+ trait B {
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+ fn b ( & self ) -> Self ;
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+ }
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+
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+ default impl < T =i32 > B for Option < T >
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+ where T : Default
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+ {
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+ fn b ( & self ) -> Option < T > {
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+ Some ( T :: default ( ) )
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+ }
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+ }
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+
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+ impl B for Option < String >
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+ {
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+ fn b ( & self ) -> Option < String > {
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+ Some ( "special" . into ( ) )
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+ }
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+ }
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+
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+ fn main ( ) {
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+ let x = None ;
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+ // Even with defaults, the concrete impl is prefered,
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+ // the defaults are simply ignored.
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+ foo ( x. b ( ) ) ;
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+ }
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+
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+ fn foo < T =i32 > ( a : Option < T > )
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+ where T : Debug {
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+ assert_eq ! ( format!( "{:?}" , a. unwrap( ) ) , "\" special\" " ) ;
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+ }
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