Here, you’ll learn how data classes enable you to write code that’s cleaner and more concise than you ever dreamed was possible.

1. 本句，learn 是“获悉；知道”；不是“学习；学会”。

2. 整个划线部分是 learn 的宾语从句。 how data classes enable you to write code that’s cleaner and more concise than you ever dreamed，是宾语从句的主语； was possible 是系表。

3. 这里，how 实际等于 that 的用法，引导主语从句。how 暗含“方式”，that 没有语义。这里 how 就按 that 理解就行了，或者换成 the way。其实这三种结构，表意是一样的，相等的：

That you can do it is possible.

How you can do it is possible.

The way you can do it is possible.

4. 我用两个简单的句子演示：

You will learn how you can guess the meaning of words.
You will learn how you can guess the meaning of words is possible.

你将学会如何猜出单词的意思。
你会知道，你猜出单词的意思是可能的。

我对这个句子的分析与刘老师不同。

了解这种句子结构，网友首先应该有“嵌入分句”（embedded clause）的概念。即一个分句被嵌入到另一个分句中并在该分句中作一个分句成分。

答疑网实际上已经讨论过三种嵌入式分句：

1 嵌入式定语从句：

This is the book (which) my teacher says is important.

which is important这个分句嵌入到my teacher says这分句中，作该分句的宾语从句。嵌入式定语从句中，which作is important的主语，也是可以省略的。网友的下面句子就是省略了作主语的关系代词that：

That was definitely something （that）she never dreamed was possible.

that was possible分句嵌入到she never dreamed分句中，并作该分句的宾语从句。that虽然作主语，也可以省略。

2 嵌入式名词性关系分句：

This is what he thinks is important.

what is important是 he thinks的宾语从句。what=the thing which, 所以本句等于：

This is the thing which he thinks is important. 这就成了嵌入式定语从句了。

3 嵌入式疑问分句：

Who do you think can do this job?

who can do this job这个疑问分句嵌入到do you think分句中，并在该分句中作宾语从句。

了解了以上三种嵌入式分句，就不难理解其实也存在嵌入式比较分句：

4 嵌入式比较分句：

Tom is taller than I believe John is.

我们把than分析为比较代词。than在I believe的宾语从句中作表语。即比较分句嵌入到I believe分句中作了宾语从句。

This code is more concise than I think is possible.

than is possible 这个分句嵌入到I think 分句中，作该分句的宾语从句。

至此，网友应该已经明白，提问中的句子其实是一个嵌入式比较分句：

Here, you’ll learn how data classes enable you to write code that’s cleaner and more concise than you ever dreamed was possible.

划线部分than was possible为嵌入式比较分句，作you ever dreamed的宾语从句，than为was possible 的主语。