Add feature_count{,_force} and implement Iterator::size_hint #108
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src/vector/layer.rs
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| @@ -112,6 +112,19 @@ impl<'a> Layer<'a> { | |||
| Ok(()) | |||
| } | |||
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| pub fn feature_count(&self) -> Option<u64> { | |||
| let rv = unsafe { gdal_sys::OGR_L_GetFeatureCount(self.c_layer, 0) }; | |||
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I'm not a big gdal user - and didn't know what "force" or negative numbers meant in this context. It might be worth surfacing some of the documentation, otherwise users of this crate have to defer to the rust source to see which upstream method we're calling and then look up the upstream docs for that method.
from https://gdal.org/api/vector_c_api.html#_CPPv421OGR_L_GetFeatureCount9OGRLayerHi
If bForce is FALSE, and it would be expensive to establish the feature count a value of -1 may be returned indicating that the count isn’t know. If bForce is TRUE some implementations will actually scan the entire layer once to count objects.
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yes, some documentation would be great
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I was just following the example of the surrounding code ;)
On second thought, I'm not happy with the API that I wrote here. It's better than the existing get_extent(&self, force: bool), but I think feature_count and feature_count_force should be named try_feature_count and feature_count, respectively. This is consistent with TryInto and Into from the standard library.
I'll send a separate API-breaking PR to use that pattern for get_extent too. Ah, this 0.x version number is so liberating!
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i think it is a good idea to split it into two methods. I guess we should wait for the get_extent change before we release a new version.
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Nice for progress bars and just generally good to have proper size_hints if cheap to compute.