Reuse same object for tagged template quasis. #67
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Spec tagged template literals pass the same object to each invocation of the template tag function. This way that object can be used as a cache key, for example, using a `Map`, so that parsing of the string contents can be cached. This patch changes the tagged template literal transform to declare a frozen top-level array with the quasi strings, and passes that array to each invocation. I think it's important to adhere to the spec re: freezing, because otherwise people might try to attach properties to the object itself as a sort of caching mechanism, which doesn't work in spec tagged template literals. I'm unsure if this is the _best_ way to declare a top-level variable, but it seems to work OK :)
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At least my Node v6.12.0 and my Firefox 57 seem to intern the arrays, so that even different call sites pass the same object: let x;
function f(r) { x = x || r; console.log(x === r) };
f`a${ 1 }`; // true
f`a${ x }`; // true
f`b`; // false
f(["a"]); // false
f`a${ 5 }` // true |
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oh yeah that's a great catch, thanks! 6272cc0 only creates a new |
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Wow, that was fast! This doesn't work across multiple files, but otherwise it's great, and I doubt there is a reasonable way to make that work. |
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yeah, exactly—and even so, this will still allow template tags to save a lot of time by reducing parsing to just once per template per file, instead of on every single call. |
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Ok, I just went ahead and merged this, it's definitely an improvement :) Thanks for your contribution! |
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I just pushed 7583ae8, which fixed this code putting definitions before directives. |
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oops! thanks! |
bublejs/buble#67 changed Bublé template strings to compile similarly to Babel ones, for spec reasons. With this patch, the new style as well as the old style are detected correctly.
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Actually, Runtime Semantics: GetTemplateObject step 4.a specifies that each parse node gets its own template object, contrary to what V8 does. See also tc39/test262#972. |
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O, that's nice. I can prepare a PR that basically reverts the second commit from this one today, I think. |
Spec tagged template literals pass the same object to each invocation of
the template tag function. This way that object can be used as a cache
key, for example, using a
Map, so that parsing of the string contentscan be cached.
This patch changes the tagged template literal transform to declare a
frozen top-level array with the quasi strings, and passes that array to
each invocation. If this lands I think it's important to adhere to the spec re:
freezing, because otherwise people might try to attach properties to the
object itself as a sort of caching mechanism, which doesn't work in spec
tagged template literals.
I'm unsure if this is the best way to declare a top-level variable,
but it seems to work OK :)