Add parsing of pointers #63
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Pointers can be useful if we want to allow using types recursively directly (i.e. not as an array or mapping), for example to express tree structures (decision trees, composite types, etc.).
VPanteleev-S7
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source/configy/read.d
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| else static if (is(FR.Type == T*, T)) | ||
| { | ||
| // Allocate and parse pointers' values. | ||
| auto value = new T; | ||
| *value = node.parseField!(NestedFieldRef!(T, FR))( | ||
| path, T.init, ctx); | ||
| return value; | ||
| } |
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That doesn't quite work for const / immutable types though. A lot of the code in this module is convoluted to allow for const & immutable values to be used.
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Good catch. Fix pushed, not sure if that fix is the best way?
source/configy/test.d
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| { | ||
| static struct N { | ||
| @Optional int value; | ||
| @Optional N* left, right; |
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I think pointers should always be optional. I can't see a situation where they wouldn't be.
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I can think of one - when using mutually recursive types, only one point of recursion might be optional, e.g.:
import configy.attributes;
/// Node for an AST for some language that uses infix operators.
struct Node {
// Only one of these must be set.
@Optional BinaryExpression* addition;
@Optional BinaryExpression* subtraction;
// ...
}
struct BinaryExpression {
// You've chosen which kind of expression this is.
// Now, you MUST specify the operands, so these are not optional:
Node* left, right;
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I guess left and right could just be Node. Seems a bit weird though, with how ASTs are usually represented in memory. Might be asymmetric with other parts where Node values are optional.
I'm curious to know why? I agree that pointers are not ideal, but my main issues with using them in this context would be that they come bundled with some semantics (pointer arithmetic, indexing, segmentation faults on null dereferences) that are not helpful here. |
Pointers can be useful if we want to allow using types recursively directly (i.e. not as an array or mapping), for example to express tree structures (decision trees, composite types, etc.).