docs: explain what world-age issue is #362
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timholy
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Jun 18, 2022
docs/src/world_age_issue.md
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| The second `f()` works because this time you're running a recompiled version of `f()` in the latest | ||
| world age with the necessary `size(::IndirectArray)` defined. | ||
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| ## Solution |
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Suggested change
| ## Solution | |
| ## Solutions | |
| ### `Base.invokelatest` | |
| One solution is to make the call to `size` via `Base.invokelatest`, | |
| which exists explicitly to work around this world-age dispatch problem. Literally, `invokelatest` | |
| dispatches the supplied call using the latest world age (which may be newer than when you | |
| typed `f()` at the REPL). **In a fresh Julia session**, | |
| ``julia | |
| julia> using FileIO | |
| julia> f() = Base.invokelatest(size, load("indexed_image.png")) | |
| f (generic function with 1 method) | |
| julia> f() | |
| (4, 4) | |
| `` | |
| !!! note | |
| In step 3 above ("FileIO calls the appropriate PNG-specific `load` function in PNGFiles"), | |
| the call to the `load` function defined in PNGFiles is made via `invokelatest`. | |
| Otherwise, even ordinary interactive usage of FileIO (without burying `load` inside a function) | |
| would cause world-age errors. | |
| !!! warning | |
| Using `invokelatest` slows your code considerably. Use it only when absolutely necessary. | |
| ### Eagerly load the required packages first |
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You're going to have to change double-backticks to triple-backticks; unfortunately GitHub terminates the suggestion on the first triple-backticks it finds.
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A tip is to wrap the block with four backticks
Co-Authored-by: Tim Holy <tim.holy@gmail.com>
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@timholy thanks for the heavy rewrite, much clearer! |
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