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What does [..] mean for Rust slices and what is it called? [duplicate]

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0

This question already has an answer here:

• 
  What does the “two periods” operator mean in the context of a subscript inside of square brackets?
  
  2 answers
  
  

I've found this example in a README:

use std::env;

fn main() 
 let filename: &str = &env::args().nth(1).unwrap()[..];
 let filename2: &str = &env::args().nth(1).unwrap();
 println!(":?", filename);
 println!(":?", filename2)

I'm interested in the first line: let filename ....

What does the [..] after the unwrap mean?

The second line let filename2 ... is my own test that both filename and filename2 are the same, or do I miss something?

What is this [..] called?

string rust slice

share|improve this question

edited Mar 25 at 15:16

Shepmaster

163k16338485

asked Mar 22 at 12:53

zzeroozzeroo

3,33912536

marked as duplicate by Shepmaster rust
Users with the  rust badge can single-handedly close rust questions as duplicates and reopen them as needed.

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Mar 22 at 13:37

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It's a range.
  
  – jonrsharpe
  Mar 22 at 12:55
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Pedantically .. is a RangeFull, [] is the indexing / slicing syntax. See also Appendix B: Operators and Symbols
  
  – Shepmaster
  Mar 22 at 13:42
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It is not useless — it converts a &String into a &str in this case. The : &str isn't needed, but it's probably to show the types to make it easier for people to understand the types in play. Your second line does the same thing via Deref coercion.
  
  – Shepmaster
  Mar 25 at 15:16
  
  

  
  
  
  

add a comment | 

0

This question already has an answer here:

• 
  What does the “two periods” operator mean in the context of a subscript inside of square brackets?
  
  2 answers
  
  

I've found this example in a README:

use std::env;

fn main() 
 let filename: &str = &env::args().nth(1).unwrap()[..];
 let filename2: &str = &env::args().nth(1).unwrap();
 println!(":?", filename);
 println!(":?", filename2)

I'm interested in the first line: let filename ....

What does the [..] after the unwrap mean?

The second line let filename2 ... is my own test that both filename and filename2 are the same, or do I miss something?

What is this [..] called?

string rust slice

share|improve this question

edited Mar 25 at 15:16

Shepmaster

163k16338485

asked Mar 22 at 12:53

zzeroozzeroo

3,33912536

marked as duplicate by Shepmaster rust
Users with the  rust badge can single-handedly close rust questions as duplicates and reopen them as needed.

StackExchange.ready(function()
if (StackExchange.options.isMobile) return;

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StackExchange.helpers.removeMessages();

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);
Mar 22 at 13:37

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It's a range.
  
  – jonrsharpe
  Mar 22 at 12:55
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  Pedantically .. is a RangeFull, [] is the indexing / slicing syntax. See also Appendix B: Operators and Symbols
  
  – Shepmaster
  Mar 22 at 13:42
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It is not useless — it converts a &String into a &str in this case. The : &str isn't needed, but it's probably to show the types to make it easier for people to understand the types in play. Your second line does the same thing via Deref coercion.
  
  – Shepmaster
  Mar 25 at 15:16
  
  

  
  
  
  

add a comment | 

This question already has an answer here:

• 
  What does the “two periods” operator mean in the context of a subscript inside of square brackets?
  
  2 answers
  
  

I've found this example in a README:

use std::env;

fn main() 
 let filename: &str = &env::args().nth(1).unwrap()[..];
 let filename2: &str = &env::args().nth(1).unwrap();
 println!(":?", filename);
 println!(":?", filename2)

I'm interested in the first line: let filename ....

What does the [..] after the unwrap mean?

The second line let filename2 ... is my own test that both filename and filename2 are the same, or do I miss something?

What is this [..] called?

string rust slice

share|improve this question

edited Mar 25 at 15:16

Shepmaster

163k16338485

asked Mar 22 at 12:53

zzeroozzeroo

3,33912536

use std::env;

fn main() 
 let filename: &str = &env::args().nth(1).unwrap()[..];
 let filename2: &str = &env::args().nth(1).unwrap();
 println!(":?", filename);
 println!(":?", filename2)

share|improve this question

edited Mar 25 at 15:16

Shepmaster

163k16338485

asked Mar 22 at 12:53

zzeroozzeroo

3,33912536

share|improve this question

edited Mar 25 at 15:16

Shepmaster

163k16338485

asked Mar 22 at 12:53

zzeroozzeroo

3,33912536

edited Mar 25 at 15:16

Shepmaster

163k16338485

edited Mar 25 at 15:16

Shepmaster

163k16338485

asked Mar 22 at 12:53

zzeroozzeroo

3,33912536

asked Mar 22 at 12:53

zzeroozzeroo

3,33912536

1 Answer
1

active

oldest

votes

3

A string can be used as an array of bytes. This addition does strictly nothing:

#![feature(core_intrinsics)]

fn print_type_of<T>(_: &T) 
 println!("", unsafe std::intrinsics::type_name::<T>() );


fn main() 
 let x = "abc";

 print_type_of(&x); // &str

 let x = &x[..];

 print_type_of(&x); // &str

[..] takes the full range, and & takes a reference to it.

share|improve this answer

answered Mar 22 at 12:58

French BoiethiosFrench Boiethios

11.4k44081

add a comment | 

3

A string can be used as an array of bytes. This addition does strictly nothing:

#![feature(core_intrinsics)]

fn print_type_of<T>(_: &T) 
 println!("", unsafe std::intrinsics::type_name::<T>() );


fn main() 
 let x = "abc";

 print_type_of(&x); // &str

 let x = &x[..];

 print_type_of(&x); // &str

[..] takes the full range, and & takes a reference to it.

share|improve this answer

answered Mar 22 at 12:58

French BoiethiosFrench Boiethios

11.4k44081

add a comment | 

3

A string can be used as an array of bytes. This addition does strictly nothing:

#![feature(core_intrinsics)]

fn print_type_of<T>(_: &T) 
 println!("", unsafe std::intrinsics::type_name::<T>() );


fn main() 
 let x = "abc";

 print_type_of(&x); // &str

 let x = &x[..];

 print_type_of(&x); // &str

[..] takes the full range, and & takes a reference to it.

share|improve this answer

answered Mar 22 at 12:58

French BoiethiosFrench Boiethios

11.4k44081

add a comment | 

A string can be used as an array of bytes. This addition does strictly nothing:

#![feature(core_intrinsics)]

fn print_type_of<T>(_: &T) 
 println!("", unsafe std::intrinsics::type_name::<T>() );


fn main() 
 let x = "abc";

 print_type_of(&x); // &str

 let x = &x[..];

 print_type_of(&x); // &str

[..] takes the full range, and & takes a reference to it.

share|improve this answer

answered Mar 22 at 12:58

French BoiethiosFrench Boiethios

11.4k44081

#![feature(core_intrinsics)]

fn print_type_of<T>(_: &T) 
 println!("", unsafe std::intrinsics::type_name::<T>() );


fn main() 
 let x = "abc";

 print_type_of(&x); // &str

 let x = &x[..];

 print_type_of(&x); // &str

share|improve this answer

answered Mar 22 at 12:58

French BoiethiosFrench Boiethios

11.4k44081

answered Mar 22 at 12:58

French BoiethiosFrench Boiethios

11.4k44081

answered Mar 22 at 12:58

French BoiethiosFrench Boiethios

11.4k44081