coercion

The following code won't compile due to two instances of this error: error[E0277]: the trait bound Self: std::marker::Sized is not satisfied I don't understand why Sized is required in this instance as both &self and &Any are pointers and the operation does not require knowledge of the size of the structure that implements the trait, it only requires knowledge of the pointer itself and the type it is converting from and to, which it will have because &self is generic when implemented inside a trait. I think this may be an instance of the compiler enforcing unnecessary constraints and I've

I was wondering a few things about coercion. When you do: 1 == true // true Which one is coerced into which one ? is it the left one or the right one ? When you do undefined == null // true How does it work exactly ? In which order does it try to convert it ? By instance: 1) String(undefined) == String(null) // false 2) Number(undefined) == Number(null) // false 3) Boolean(undefined) == Boolean(null) // true Does it first try to coerce the left side operand ? then the right ? then both ? EDIT: As explained in the comments: "not a duplicate. While both questions are about type coercion, this

I need to convert a multi-row two-column data.frame to a named character vector. My data.frame would be something like: dd = data.frame(crit = c("a","b","c","d"), name = c("Alpha", "Beta", "Caesar", "Doris") ) and what I actually need would be: whatiwant = c("a" = "Alpha", "b" = "Beta", "c" = "Caesar", "d" = "Doris") Use the names function: whatyouwant <- as.character(dd$name) names(whatyouwant) <- dd$crit as.character is necessary, because data.frame and read.table turn characters into factors with default settings. If you want a one-liner: whatyouwant <- setNames(as.character(dd$name), dd

Please read to the end before deciding of voting as duplicate... I have a type that implements an implicit cast operator to another type: class A { private B b; public static implicit operator B(A a) { return a.b; } } class B { } Now, implicit and explicit casting work just fine: B b = a; B b2 = (B)a; ...so how come Linq's .Cast<> doesn't? A[] aa = new A[]{...}; var bb = aa.Cast<B>(); //throws InvalidCastException Looking at the source code for .Cast<> , there's not much magic going on: a few special cases if the parameter really is a IEnumerable<B> , and then: foreach (object obj in source)

Consider the array x = np.array(['1', '2', 'a']) Tying to convert to a float array raises an exception x.astype(np.float) ValueError: could not convert string to float: a Does numpy provide any efficient way to coerce this into a numeric array, replacing non-numeric values with something like NAN? Alternatively, is there an efficient numpy function equivalent to np.isnan , but which also tests for non-numeric elements like letters? You can convert an array of strings into an array of floats (with NaNs) using np.genfromtxt : In [83]: np.set_printoptions(precision=3, suppress=True) In [84]: np

In the process of (mostly) answering this question, I stumbled across something that I feel like I really should already have seen before. Let's say you've got a list: l <- list(a = 1:3, b = letters[1:3], c = runif(3)) Attempting to coerce l to various types returns an error: > as.numeric(l) Error: (list) object cannot be coerced to type 'double' > as.logical(l) Error: (list) object cannot be coerced to type 'logical' However, I'm apparently allowed to coerce a list to character, I just wasn't expecting this result: > as.character(l) [1] "1:3" [2] "c(\"a\", \"b\", \"c\")" [3] "c(0

Why are both &[u8] and &[u8; 3] ok in this example? fn main() { let x: &[u8] = &[1u8, 2, 3]; println!("{:?}", x); let y: &[u8; 3] = &[1u8, 2, 3]; println!("{:?}", y); } The fact that &[T; n] can coerce to &[T] is the aspect that makes them tolerable. — Chris Morgan Why can &[T; n] coerce to &[T] ? In what other conditions does this coercion happen? Chris Morgan [T; n] is an array of length n , represented as n adjacent T instances. &[T; n] is purely a reference to that array, represented as a thin pointer to the data. [T] is a slice, an unsized type; it can only be used through some form of

I'm reading Hadley Wickham's Advanced R section on coercion, and I can't understand the result of this comparison: "one" < 2 # [1] FALSE I'm assuming that R coerces 2 to a character, but I don't understand why R returns FALSE instead of returning an error. This is especially puzzling to me since -1 < "one" # TRUE So my question is two-fold: first, why this answer, and second, is there a way of seeing how R converts the individual elements within a logical vector like these examples? jdharrison From help("<") : If the two arguments are atomic vectors of different types, one is coerced to the