Using Generic types at runtime

TypeScript types are compile time only. Generic parameters only exist in the _type_ declaration space and cannot be used as is in the _variable_ declaration space. Mention the workarounds :rose:

This is good section to put it into : https://basarat.gitbooks.io/typescript/content/docs/project/declarationspaces.html

Start with the declarationspaces section at https://basarat.gitbooks.io/typescript/content/docs/project/declarationspaces.html and review how it distinguishes type and variable declaration spaces. Document that generic parameters exist only at compile time and explain the relevant workarounds. Done means the section clearly covers runtime limitations and practical alternatives.

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