make string definition work on call overloadable structs

[KristofferC]

No description provided.

[codecov]

Codecov Report

Merging #89 (a00b0ff) into master (c309a9c) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
+ Coverage   88.38%   88.42%   +0.04%     
==========================================
  Files           3        3              
  Lines         241      242       +1     
==========================================
+ Hits          213      214       +1     
  Misses         28       28              

Impacted Files	Coverage Δ
src/utils.jl	80.80% <100.00%> (+0.19%)	⬆️

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[timholy]

Thanks!