Theo's Typesafe Cult•2y ago

TS Unchecked Indexed Access

Hey guys, I have a question about ts. I have a "noUncheckedIndexedAccess": true in my tsconfig. I am trying to make a function (well, chatgpt helped me create a function lol) that is a calculator to get Levenshtein distance (basically for a fuzzy search, but it's not the main point). as a part of it I have a for loop along the lines of this

const res: number[][] = [];
for (let i = 0; i < 10; ++i) {
  res[i] = [];
  res[i][0] = i;
}

const res: number[][] = [];
for (let i = 0; i < 10; ++i) {
  res[i] = [];
  res[i][0] = i;
}

So I get the error saying res[i] Object is possibly undefined. - on line

  res[i][0] = i;

  res[i][0] = i;

So my question is this: is there a way for compile to get it correctly as I literally define res[i] on the line before? or is it some sort of a bug on my part? or is it something not possible? P.S. if you are interested here's the full function

function levenshteinDistance(a: string, b: string): number {
  const m = a.length;
  const n = b.length;
  const dp: number[][] = [];

  for (let i = 0; i <= m; i++) {
    dp[i] = [];
    dp[i][0] = i;
  }

  for (let j = 1; j <= n; j++) {
    dp[0][j] = j;
  }

  for (let i = 1; i <= m; i++) {
    for (let j = 1; j <= n; j++) {
      if (a[i - 1] === b[j - 1]) {
        dp[i][j] = dp[i - 1][j - 1];
      } else {
        dp[i][j] = Math.min(
          dp[i - 1][j] + 1, // deletion
          dp[i][j - 1] + 1, // insertion
          dp[i - 1][j - 1] + 1 // substitution
        );
      }
    }
  }

  return dp[m][n];
}

function levenshteinDistance(a: string, b: string): number {
  const m = a.length;
  const n = b.length;
  const dp: number[][] = [];

  for (let i = 0; i <= m; i++) {
    dp[i] = [];
    dp[i][0] = i;
  }

  for (let j = 1; j <= n; j++) {
    dp[0][j] = j;
  }

  for (let i = 1; i <= m; i++) {
    for (let j = 1; j <= n; j++) {
      if (a[i - 1] === b[j - 1]) {
        dp[i][j] = dp[i - 1][j - 1];
      } else {
        dp[i][j] = Math.min(
          dp[i - 1][j] + 1, // deletion
          dp[i][j - 1] + 1, // insertion
          dp[i - 1][j - 1] + 1 // substitution
        );
      }
    }
  }

  return dp[m][n];
}

and I know I can cast types, but I want to do it without 'as ...'

3 Replies

bakdaddyOP•2y ago

bump

thevalorised•2y ago

since res[i] is an object you can create another reference to it and check it with an if statement like

const refToInner = res[i];
if(refToInner) {
  refToInner[0] = i;
}

const refToInner = res[i];
if(refToInner) {
  refToInner[0] = i;
}

But I would recommend just pushing the values to the array instead of setting the items.

const res: number[][] = [];
for (let i = 0; i < 10; ++i){
  res.push([i])
}

const res: number[][] = [];
for (let i = 0; i < 10; ++i){
  res.push([i])
}

bakdaddyOP•2y ago

thanks, that's what I kinda thought, just make a new reference and check it

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TS Unchecked Indexed Access