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I tried this but it doesn't work.
let result: u8 = opcode & 0xff;
the thing is opcode & 0xff will always return something in 0 -> 255 which would always fit in the u8 but the compiler raise the error expected u8 but found u16. Why did Rust raise the error?
Rust doesn't cast between types implicitly, you have to be explicit about the cast using the as keyword:
let result = opcode as u8;
Note that you can omit the AND operator, the as keyword will automatically truncate the number when converting from a larger type.
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I'm new to rust and tried writing a function that adds all digits at the uneven positions together (For context: I'm trying to solve this Daily programmer #370. But somehow my results are off by a bit and I can't wrap my head around what#s going on.
number.to_string().chars()
.enumerate()
.filter(|(i, _)| i % 2 != 0)
.map(|(_, c)| c as u64 - 48)
.sum::<u64>()
Now if I input 4210000526 I get 13 as a result, although I should get 15. For some reason this only happens with a filter for uneven positions, "i % 2 == 0" works perfectly fine.
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See the code:
struct A {}
impl A {
fn a(&self) {}
}
pub fn main() {
let a = A {};
a.a();
A::a(&a);
}
Why a.a() doesn't need the & while A::a(&a) needs? What's the difference?
In Rust, a.a() is syntax sugar for A::a(&a), so a does get borrowed in both calls. The dot operator does a lot more as well, you can read about that here.
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I just want to play with DEADBEEF like this:
println!("0x{:X}", "0xDEADBEEF");
And I got this:
the trait bound str: std::fmt::UpperHex is not satisfied
the trait std::fmt::UpperHex is not implemented for str
What I do wrong, why I am not able to print the value?
Just do not wrap the value into a str, and use a proper type marker, u32 would do:
fn main() {
println!("0x{:X}", 0xDEADBEEFu32);
}
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I'm wondering after why these assertions are passing
token_generated = ".eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJlbWFpbCI6ImRhdmlkLmJhcnJhdEBub3ZhcnRpcy5jb20iLCJleHBpcmF0aW9uIjoiMjAxOC0wMS0xMVQyMjowNTozMi44MjIwNDUifQ.jalHa2ZpnxH00v3tP6CKL3nUkiTMt4rsjo6P3DM32DA"
self.assertTrue(type(token_generated) == str)
self.assertTrue(type(token_generated) == bytes)
Both tests pass, but I don't understand why my token variable can have two types as it should be only a String
Because when I'm printing the type of token_generated
print (type(token_generated))
I got that : .<type 'str'>
Assuming you are using Python 2, the str- and bytes-type are actually the same
>>> bytes is str
True
Therefore they are also equal.
If you want to know if token is a valid utf8-string, you should decode it:
token = '\xff'
try:
token.decode('utf8')
except UnicodeDecodeError:
print "The bytes are just bytes, or maybe some other encoding"
else:
print "The bytes are a utf8 string, hooray"
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In rust I have the following
use std::io;
fn lookup(host: &str, timeout_duration: time::Duration) -> io::IOResult<Vec<ip::IpAddr>>{
// Some blah implementation here...
}
However I'm getting a compilation error.
src/hello.rs:7:60: 7:89 error: use of undeclared type name `io::IOResult`
I'm confused because there is clearly an IOResult struct in the std::io namespace (as of November 16 2014): http://doc.rust-lang.org/std/io/type.IoResult.html
What am I doing wrong?
Don't capitalize the name (doh): IOResult -> IoResult
The signature is
type IoResult<T> = Result<T, IoError>;