If I may, let me try again and make the case for a more robust data structure
for callSiteId. The reason of my insistence is that I've used a similar array
encoding in the past (for message templates) and it has bitten me: people
always got indices wrong (in a small library that students of mine used). A
list of tokens was a more robust solution and might work for quasis, if an
indirection is introduced. Many people will use these data structures, so they
should be as fool-proof as possible.
########## Proposal ##########
handler`aaa${foo}\nbbb`
desugars to:
const callSiteId1234 = {
tokens: [
{ raw: "aaa", cooked: "aaa" },
{ key: "foo", valueIndex: 0 },
{ raw: "\\nbbb", cooked: "\nbbb" },
]
};
handler(callSiteId1234, [foo]);
########## Using the proposal for the default impl. ##########
// default quasi tag impl. with data structures as shown above
function (callSiteId, substArray) {
var out = [];
callSiteId.tokens.forEach(function(token) {
out.push(token.raw !== undefined ? token.raw :
substArray[token.valueIndex]);
});
return out.join("");
}
// For comparison: default quasi tag impl. from spec
function (callSiteId /* , ...substitutions */) {
var rawStrs = callSiteId.expandedLP;
var out = [];
var i = 0, k = -1, n = rawStrs.length - 1;
while (i < n) {
out[++k] = rawStrs[i];
out[++k] = arguments[++i];
}
out[++k] = rawStrs[n];
// As per the original Array.prototype.slice and Array.prototype.join.
return out.join("");
}
########## Alternative: types for tokens ##########
One could also introduce types for tokens. Then the iteration body becomes:
out.push(token instanceof LiteralSection ? token.raw :
substArray[token.valueIndex]);
This is bike-shedding, but I’d also prefer "uninterpreted" and "interpreted"
instead of "raw" and "cooked".
--
Dr. Axel Rauschmayer
a...@rauschma.de
twitter.com/rauschma
home: rauschma.de
blog: 2ality.com
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